What is the differentiator between these two phrases?
These are not two variants of the same phrase. "Of" is simply a preposition.
- "... that which you own ..."
→ You own something.
- "... that of which you are the owner ..."
→ You are the owner of something, that's where the preposition comes from.
Similarly, you could encounter "that in which you", "that under which you", "that from which you", and theoretically even "that out from behind which you". The possibilities are (almost) endless!
Maybe "-a vehicle- is something of that which is owned" or, "-emotions- are something that with of which you feel". "42, is that of which what is still unknown" "I need an answer, but one with that of which has what would be useful"