Under a strict reading of the rules, the Will save is for the caster. Something was clearly missed in editing, however, which raises the question of how it was supposed to be written. I see three main possibilities:
(1) The inclusion of a saving throw line was an error. Spells with "Range personal" and "Target you" typically do not have saving throws if only because anyone casting the spell presumably wants its effect and would simply choose to fail the save. There are exceptions, such as form of the dragon (which has a save for the breath weapon). But when such exceptions appear, they are explained in the spell's description.
(2) The save is supposed to be "Will negates (harmless)." Plenty of spells have this in their saving throw line, including other illusion (glamer) spells such as blur, displacement, and all three forms of invisibility. Since the effect is purely beneficial with no downside for the spell's target, one might expect any save associated with it to have the "harmless" tag.
(3) The save is supposed to be "Will disbelief (if interacted with)." This is reasonably common for illusion (figment) spells and can be found in the save line for illusion spells of all types except for patterns (e.g., silent image, hallucinatory terrain, phantasmal killer, and shades). There is even a figment spell with a range of "personal" and a target of "you" that has "Will disbelief" in the save line (illusion of calm), though the Will save only occurs when the spell's target is hit.
In the end, none of us know what it was actually supposed to be. Nevertheless, I'd like to make a brief and admittedly circumstantial case for option (1). First, as already noted, spells with "Range personal" and "Target you" typically do not even have a line for saving throws or spell resistance. Yes, there are deviations from this norm (e.g., form of the dragon). And yes, those deviations occur when the spell has an effect on another creature (which raiment of command undoubtedly does). But the effects that receive saves are typically direct effects (the breath weapon granted by form of the dragon is a direct attack), and the deviations are explained in the spell's description. Raiment of command has an indirect effect on other creatures (it makes the target seem more impressive, which in turn makes other creatures act differently around the target), and there is nothing in the spell's description to explain what effect a successful saving throw might have.
Second, "Will negates (harmless)" is essentially meaningless on a spell that is not subject to spell resistance and can only target the caster. It makes sense on spells that can be cast on targets other than the caster (since maybe they'll want to resist the spell, such as an undead creature saving against cure light wounds), but a personal spell with "Saving Throw Will negates (harmless)" and "Spell Resistance no" might as well not have a saving throw/spell resistance line at all. But of course, that is tantamount to endorsing option (1): the inclusion of a saving throw line was an error. Given that raiment of command is not subject to spell resistance, then, it is unlikely that option (2) is correct.
Third, there's no reason to think that raiment of command must allow a saving throw. Plenty of spells give bonuses to skills—including the skills boosted by raiment of command—without offering a saving throw to those with whom the caster might subsequently interact. Enhanced diplomacy is a cantrip, but it still gives a +2 competence bonus on a single Diplomacy or Intimidate check. Then there's aspect of the nightingale, chastise, and of course glibness. In fact, we might not even be having this conversation if raiment of command was a transmutation spell. Everyone might have just assumed that the saving throw line was in error.
But the mere fact that a spell comes from the illusion school doesn't entail that it must (or even just should) allow a saving throw. Not all illusion spells allow saving throws. You can't disbelieve the illusory doubles created by mirror image, for example, even though they are figments. Raiment of command is certainly more powerful than enhanced diplomacy (a cantrip). It is also more powerful than aspect of the nightingale or chastise (both 1st-level spells). But it is probably not as powerful as glibness (a 3rd-level spell). Given that it is a 2nd-level spell, this all seems perfectly in order. And since none of the other spells allow the caster's opponents to save against their effects, there's no reason to think that raiment of command must grant such a save either.
To be sure, none of this is dispositive. The entire case rests on comparisons to other spells, which are not guaranteed to be consistent across the board in terms of either design or power level. Given that everyone else posting responses seemed to be more or less assuming something like option (3), however, I thought it worthwhile to at least present an argument for an alternative reading of the spell. I'm sure there's plenty of counterarguments that could (and perhaps will) be made. But I think there's at least a decent prima facie case for not giving a saving throw to those who are interacting with someone under the effects of this spell.
