Frank Luke's answer is clear enough to realize Cain is Adam's son, no question about that. I want to address something else you state:
Assuming that Cain is the person that Jesus is referring to
I would not assume that, nor would I argue that is correct. I take Jesus's statement as wholly referencing "the Devil" himself (just as the verse states). He was a murderer from the beginning, because it is he who sought Adam's death (and thus mankind's death), and succeeded in bringing it about, through the temptation of Eve. He is also the "father of lies," because he was the first to lie.
So when Jesus is accusing those Jews who sought "to kill" him because his "word had no place in" them (v.37) of belonging "to your father,the Devil," (v.44), the context tells us the relationship. They were not believing the truth (Christ's "word"), and in fact actively opposing the truth (so they were being/promoting liars), while also seeking Christ's death (wanting to do murder).
In this context, Jesus is asserting that in being obedient to lying and murder, they are following after the Devil, and as such demonstrating that he, and not God, is their (spiritual) father, who they are imitating (v.38).
Christ had already acknowledged that physically they were of Abraham (v.37), but spiritually (as in who they were obeying), they were not of Abraham (v.39), because they were not acting like Abraham did. They were seeking to kill Jesus because he spoke truth to them (v.40), such desire to kill God's messenger was something Abraham never did. Rather, if God were their father (v.41), they would love Christ (v.42). But they do not love Him because they really do not have God as their spiritual father, but rather the Devil (v.44).
There is nothing in the context at all to point to Cain as being referenced, and (as noted above), the Devil fits the bill as both first murderer and first liar. The term "father" is being used figuratively in the sense of the one who is obeyed, loved, and imitated (as is proper in a non-dysfunctional father/child relationship). The unbelieving were demonstrating their unbelief by not obeying, loving, and imitating God, nor His Son.