We need truth.We want the truth to match up with our desires or ideals, but in the end we all need truth. Children have mastered one method of finding true answers and understanding of any enigma: Asking questions.
If there's an afterlife, that's the mean there's a god?
Not "a god" necessary, but there would definitely have to be something greater than our understanding.
If there's a god, does that mean there's an afterlife?
No. It could even mean there's an afterlife for some, reincarnation for others, something else still for others, and nothing for some.
If there's an afterlife, could there be an afterdeath?
Umm…sure, I guess.
Is this topic beyond us?
Okay, if we've no basis whatsoever to base the afterlife off, then there are unlimited possibilities about every aspect of it! There has to be something more if we are to discover the truth, but just knowing or thinking about an infinite list of possibilities won't guide us into the answers we seek. That method may be consider a noble or an enlighten approach, but, that will overwhelm or confused us. Searching for truth is great, but it does not compare to actually finding it.
What would be valid or legitimate sources of knowledge concerning the afterlife? How would their legitimacy be judged?
Hard to say. The sources should be proven true on the things it already says. Also, if the source has made predictions, all or some of those should have come true (depending when the prediction was referring.) Also, this goes beyond natural limited of our knowledge, so the source should have some expertise on the supernatural or spiritual.