There aren't tons who would enter Mat's tent among the Band, while he's not back to camp.¸

The top officers like Talmanes or Estean might, though it's a bit odd they waited instead of just telling Lopin they wished to talk to Mat when he's back, and that it couldn't wait the next morning.

Then there's Olver, of course, though he seems to hang mostly with Juilin and Thera now. It would be odd that Juilin would wait for Mat in his tent, even more Thera.

It would be quite in Leilwyn's character to insist with Lopin to wait for Mat, if she's decided she must have a talk with him that nightm, as she would never trust Mat to come to her any time soon if she let a message to his servant. It's too much to hope we're finally rid of the woman, though! She could have sent Domon to wait for Mat too, I guess. I doubt it's either of those two, as Brandon puzzingly spoke long ago of stacking their POVs with the "Elayne, BT and miscellaneous characters", so it sounds like those two will leave Mat soon, and so they survive a while.

It can't really be Noal, unless the person in the tent isn't dead, and the Yellow Edesina (conveniently returned) will be able to save him or her.

Then there's the fact the men knew Mat was in the city, and they also knew the AS were back and waiting for him. No one mentioned that someone else was waiting for Mat, so if a visitor is in his tent, it's someone from the camp and unannounced, or it's Joline herself, while Teslyn wanted to be the first to reach Mat, so she waited outside. Of course, it's unlikely to be Joline. Her warders would have raised the alarm, and if the three of them were in the tent, no way any killer could have acted silently enough!

The most likely person to be there is Lopin himself, at least if he lives in Mat's tent. If he has his own, it's an odd time for him to have been there (though he could have been attacked much earlier, or being a good servant he was awaiting Mat's return before going to sleep). Mat has gotten to rely on a manservant a lot, so removing Lopin would be dramatic yet also bring funny situations later on.

Another who could be the visitor - though unlikely to die so soon - and is the style to be insistent enough to wait for Mat's return, is Aludra. She would also be the kind to pester him at any time of the day about the fact the making of the dragons is getting nowhere. I doubt Jordan planned to kill Aludra - but that'd be quite a plot twist (Mat has her designs - he could still build the dragons but would have to find himself an illuminator to create the munitions... at least if Aludra has not taken on a few apprentices already in preparation for mass production...)

That's about it. The rest of the people around, like band soldiers, would have no reason to wait for Mat in his tent, when he's known to be away. It sounds unlikely Lopin would let them wait in there too, or that he would let anyone wait alone in Mat's tent... making it extremely likely he is the victim, or one of the victims.

It sounds fairly unlikely to me this is an attack from the gholam. A gholam had no reason to be stealthy and silence its victim. It sounds unlikely someone could be killed by a gholam in Mat's tent without anyone screaming like pig....

That leaves an assassin DF (even Slayer himself? Why not.. Mat has either Cyndane or Moghedien or both on his back, as we know. It could actually have been an attempt by either, though it seems Moridin has ordered them to use their followers instead of attacking the two ta'veren themselves) who infiltrated the camp, and mistook the person in Mat's tent for a sign Mat was present. He entered and killed or wounded the person (the person would have to be inconscious not to scream for help afterward, if not dead though!). An assassin would be careful that a target in the middle of a military camp is silent....

Of course, if Cyndane or Moghedien is behind it, the assassin could be anyone. Easy enough for them to open a gateway in the camp for a DF or even a grey man.

It sounds to me like Mat is soon going to learn that not sleeping in the same tent every night isn't enough anymore, and that the Shadow's assassins are closing in.