If someone believes they cannot know whether or not God exists, that person is an agnostic. Your grandmother might be a devout believer, while your mom is agnostic.
In 1869, English biologist T.H. Huxley coined this noun referring to someone whose religious beliefs lie somewhere in between those of a theist and an atheist — that is, a believer and a disbeliever. Huxley combined the Greek prefix a-, meaning “not,” with gnostos, “known.” This word can be used as a noun or adjective, and it can also refer to uncertainty about questions other than the existence of God: “Some philosophers remain agnostic as to whether people have free will.”
a person who claims that they cannot have true knowledge about the existence of God (but does not deny that God might exist)
someone who is doubtful or noncommittal about something
of or pertaining to an agnostic or agnosticism
uncertain of all claims to knowledge