As we know from Episode 2: Attack of the Clones, Boba Fett was a perfect, non-accelerated-grown, clone of Jango Fett that Jango raised as his son.
"Apart from his pay, which is considerable, Fett demanded only one thing: an unaltered clone for himself. Curious, isn't it?" ―Lama Su to Obi-Wan Kenobi, referring to Fett's request for Boba Fett
Is there any in-Universe indication that Boba Fett knew that he was Jango's clone and not a biological offspring? If so, when/how did he find out?
We can confirm that, at least by 40 ABY, Boba Fett is aware of his clone lineage, in his conversation with his private Doctor, Beluine:
You give up easy, Doctor. "How long?"
"You have a standard year or two, if you take it easy. Less if you don’t."
"Don’t guess. I deal in facts."
Beluine’s eyelids fluttered in a spasm of nervous blinking. "There are always uncertainties in prognosis, sir. But the degeneration of your tissues is accelerating, even in your transplanted leg, you have recurring tumors, and the medication isn’t controlling your liver function any longer. It might have something to do with the . . . unusual nature of your background."
"That I’m a clone, you mean."
"Yes."
This conversation takes place in the Legacy of the Force EU novel Bloodlines.
I would think that most of the military clones around him would have looked very similar. This may have led him to ask about why he was different.
According to the Wookieepedia article on Boba Fett he was aware of his origins. As this isn't cited, I don't feel comfortable confirming it as in-universe truth.
Jango raised and cared for him with the assistance of the Kaminoan, Taun We, who ultimately took on the role of being a foster mother to him. Fett was aware of the fact that he was a clone of his father, however, he would often question his conception. Jango assured his son that he was a "true clone" and his real son.
I know it's an old question, but I think this is a better, canonical answer.
According to Wookieepedia, the Clone Wars TV show is still officially canon. There are several episodes in season 2 where Boba is trying to get even for Jango's death (I've watched 20-22, but I think there are some in later seasons I haven't seen yet).
In episode 20, Boba hangs out with a bunch of other clones his (apparent) age (not sure on actual ages), acting like a new recruit so he can attempt to assassinate Mace Windu. At this point, he probably is quite aware he's a clone.
In episode 21, there's an exchange between Anakin and Mace (near the end of the episode, around 18:40 on the Netflix version):
A: Whose helmet is that anyway?
M: It belongs to a bounty hunter I killed on Geonosis by the name of Jango Fett.
A: You mean the clone template?
M: Yes. Strangely enough, he had a son. Or at least a clone he regarded as a son. His name is Boba Fett.
I don't think that confirms anything not already in the prequel movies, but I haven't seen them since they were in theaters so I posted it anyways.
In episode 22, we hear an exchange between Boba and a captured clone soldier (opening scene, right after the intro prologue, 0:45 on Netflix):
B: This isn't what I wanted.
C: You don't have to do this. You're not like them. I can tell.
B: What do you know, old man?
C: I know a good soldier when I see one.
B: I'm no soldier. I'm no clone, not like those two.
It seems pretty explicit from that line he knows both that he's a clone, and that he's different from them in some ways.
