nalju'o lujvo

d1 does not knows fact(s) d2 (du'u) about subject d3 by epistemology d4

This is the proper meaning of agnostic: gnostic - knowledge, a - without. The word is not limited to just religion, and does not describe a position of belief, although it can be used in this context: agnostic theism, agnostic atheism, etc.