Neither of those options is OK. Here is the first:
Reading sharpens our mind as the truth seekers.
The "we" implied by "our" seem to share one mind, which is of course impossible. At the very least, you must write "our minds. The larger problem is that "as truth seekers" is misplaced. It seems to modify "mind"—or "minds" in my suggested revision. I suspect you want it to modify some people, perhaps all of humanity. It can only do they if they are explicitly named in the sentence.
Your revision indicates your awareness of the problem, but does not solve it.
Reading sharpens our, the truth seekers, mind
You still need the plural "minds." And a noun phrase cannot be used in apposition to a possessive adjective. You might squeak by if you make truth seekers possessive with an apostrophe: the truth seekers' minds. But it would still look and sound unnatural. I think I have seen or heard the construction, but rarely. A careful writer would avoid it.
Just to be thorough, I'll add that this will not work either:
As [the] truth seekers, reading sharpens our minds.
It would imply that reading and the truth seekers are the same thing. (I mention it only because my students write this kind of sentence often, not because you mentioned it in any way.)
It might be best to place truth seekers in a separate clause or sentence.