i get what he’s trying to say, it’s just phrased poorly and misusing “to which”. it seems like someone trying, and failing, to sound smart.

one way to see if you should use “which”, “to which” or “for which” is to put the preposition at the end and see if that sounds like something an actual human speaker of the language would say (yes, it’s technically grammatically incorrect to put a preposition at the end of a sentence, but whatever)

i.e.

he will most likely question it which i will have no reason to justify as to why i did it to

rephrasing it

he will most likely question it, for which i will have no justification