How do I find this proof?
Oh, like I said, the "proofs" are around you, even here, now, you need to understand that we currently are in a different "plane of existence" (with different physical "features" so to speak), at what we/you are without this current biological body. Here, now, the atoms of matter/energy vibrate slower than without this bio-body, and can vibrate even faster depending on the emotions (Love, gratefulness, sadness, joy, so on) one decide to create inside her/his Being.
In part, due to all of this, is that for our (so limited) physical senses many things and Beings (alive, starting by ourselves without this bio-body) are apparently invisible and seems non-existent; but that is far from the Truth...
Like I tried to describe before, one suggestion would be start by uknowledge the apparently invisible things (ghosts, any paranormal activity, psychic abilities, etc) taking each one with seriousness and researching deeply about it. Then, with the remaining that seem to be unexplained for "this world modus-operandi", review it again and always, at the same time of use your intellect, use your INTUITION... the part of your TrueSelf available now too, which has the ability to truly "know" without any intellectual analysis. Just knows, and why? because You (a part of You) already knew/experienced a given fact or information, now temporarlly "unkown" (not renembered) by your current "conscious" mind (which function with your current biological nervous system).
In short,
@EmotionlessWanderer : The proof this part of you is looking for, is already there, outside (in other experiences) and inside of Yourself (your own experiences) before encarnate in this current existence and beyond...
When I started looking for my "own proofs", long ago, I discover a website described as
Afterlife Evidence, which unified many of the apparent "invisible" or unexplained experiences, analizing them in a seriouss manner... making, for this world, visible the invisible, touchable the apparently untouchable and listened the unlistened... maybe its info can help You in find your so desired "aha moment" of memories... of Recognition... of "knowing without knowing how", You just have/feel certainty.....
Best wishes.