Isn't it important to remember that any noble can confer a knighthood? Historically anyway.
Many knights would swear fealty, not to the Emperor, but to a Baron.
In the MegaTrav setting, it's much more defined. Knights are made by Archdukes and the Emperor; lesser nobles do not have the right to create orders of knighthood or to knight folk. That model implies a great deal more central authority: you won't gain a knighthood without gaining the attention of the Emperor or one of his six Archdukes, and since they only have so many hours in the day and only so much time available for reviewing candidates, there aren't going to be too many knights.
In fact, there are likely a great deal more billionaires out there than knights:
Per MegaTrav, there are 6 Imperial domains - 6 archdukes, counting the Emperor himself as Archduke of Sylea. There are between 20 and 28 sectors with significant Imperial populations - depending on how much you'd consider "significant - and over 300 Imperial subsectors significant enough to warrant the presence of an Imperial fleet. Figure in the
rough vicinity of 300-ish dukes "associated with a subsector or sector," (some of those subsectors are rather sparse) and perhaps one to three thousand counts and marquis associated with a world or three. Barons/baronets - from here it gets speculative, but there could be five to ten times as many, they're not limited by that world or subsector bit, but by canon they're fairly significant powers in their own right - magnates and the like. All told, that's still only about 10 or 20 thousand people out of an Imperial population that must number in the trillions; in other words, out of a population the size of Earth's, there might maybe be one marquis or count and about 5 barons or so, by MegaTrav's model.
Put simply, there are a LOT more people that it would serve the Imperium to recognize - self-made billionaires, owners of important local companies, the sons and daughters of those counts and baron-magnates, and so forth. A knighthood is a handy way to do that without having in turn to deal with the heirs of THAT peer. So, figure maybe up to a hundred thousand knights Imperium-wide, maybe twice that - there might be 50 or a hundred recognized out of an Earth-size population.
By comparison, Earth today hosts over 1200 billionaires, the U.S.'s 300 million pop hosts 80 living Medal of Honor recipients, over 1200 people can claim credit for having won an Olympic gold medal over the past 20 years, and there have been 839 individuals given the Nobel prize since its inception a little over a century ago. Overall, an Imperial knighthood would be a very, very prestigious award. Assuming it survived into the far future, there'd be five to ten living Nobel-Prize recipients at any given time for each Imperial knight on Earth.
As far as I know, CT doesn't define who may or may not knight, but it would make sense for a baron to knight someone within his own entourage or someone who had done him some notable service, as a means of further ensuring that person's continued devotion to him and marking that person as someone who enjoys the baron's patronage (thereby also ensuring some other noble doesn't come along and poach this useful person away from him). That model makes sense to me for an intensely competitive political setting. Also makes for a rather lot of knights: they're an elite, but not so rare that you would fall over in a feint to meet one.
Such an honor would be recognized by the rest of the peerage, though the honoree's rank would not be very high - a person knighted by a higher noble would have higher standing in the peerage rolls. However, such fine distinctions are only of significance during formal social functions: folk are formally introduced and seated according to their rank, so the guy knighted by Baron So-and-so will find himself far back in the line behind an assortment of folk knighted by marquis, counts, dukes, or the Emperor, who all would follow the barons, who all would follow the marquis, and so forth. In more mundane settings, it's pretty much a knight is a knight is a knight, unless the knight was of a particularly distinguished order.
So, in a nutshell: you can have a universe where your character's knighthood is more prestigious than a Nobel Prize or Olympic gold medal, or you can have a universe where knighthood is more common and, while still something to be proud of, does not leave you appearing in the local newspapers every time you land on a world. The former is fun but can be very awkward in certain roleplay circumstances: someone more prestigious than a nobel prizewinner simply does not sneak into the planet unnoticed - there'll be some reporter keeping his hawk eyes on the passenger lists for noteworthy names to put in his society column.
(In either event, it is strongly advised that you NOT take the character development table as a statement of demographics - what happens there happens only for adventurers, not for everyone who goes through the service.)
I don't have GURPS Nobles, but there's an apparent canon conflict between what's been reported of GURPS and what exists in MegaTraveller. From the Imperial Encyclopedia:
"Knight: The lowest of noble ranks is knight, which is awarded by the emperor or an archduke as an honorific rank in recognition of achievement or service ... Several dozen orders of knighthood exist within the Imperium. Some are restricted to specific classes of individuals, such as members of the Imperial Family, racial Aslan, racial Vargr, or other special groups. Others are awarded for specific achievement or service or for holding specific positions within the government. Still others are broadly based orders into
which most new knights are inducted ... The most common orders of knighthood in the Imperium are the Order of the Emperor’s Guard, established in 52 and originally limited to the Emperor’s personal retainers
but now
of wide and diverse membership..."
Now, one or two hundred thousand knights among "
everal dozen orders" would indeed come to no more than a couple thousand per order. However, given the size of the Imperium I'd have to say that an order limited to 2500 members could neither be considered, "common" nor, "of wide and diverse membership." You're looking at the Emperor knighting no more than 4 or 5 persons into the order in a given month. The folk most likely to be recognized out of the trillions of Imperial citizens, and possibly tens of thousands of names put forward for recognition, would be those candidates put forward by people who had the Emperor's attention - dukes and archdukes on the frontiers, court favorites closer to home. Folk from the Imperial frontiers would have to travel a year or more to get to their knighting - in other words, rich folk with a lot of free time on their hands or folk with some pretty rich backing. Not a recipe for a very wide or diverse membership.
Thoughts?