Povu probably means "should", according to the Esperanto Bible:
However, we already have
devi. So I wonder, is there any nuance being expressed here?
I looked up PIV, Wikipedia, and ReVo, with no meaningful results.
I cannot read the text when I follow the link; is it Job 9:32?
Ĉar Li ne estas homo simile al mi,
Ke mi povu respondi al Li,
Ke ni povu ambaŭ iri al juĝo.
For he is not a man, as I am,
that I should answer him,
and we should come together in judgment. (KJV)
Here are more modern translations:
If God were human, I could answer him; we could go to court to decide our quarrel. (GNT)
He is not a mere mortal like me that I might answer him, that we might confront each other in court. (NIV)
The KJV's use of should here, to mean merely would, is not totally archaic, but it is old-fashioned. Here is a quotation from Alice in Wonderland:
"For it might end, you know, [...] in my going out altogether, like a candle. I wonder what I should be like then?"
She isn't talking about what she ought to be, but about what she would be. It was formerly laid down as a rule in English that would cannot be used after I or we; it had to be replaced by should, and that I will implies a desire. This idea originated in the distinctions made by scholars translating from Latin:
The rule is [...] to express a future event without emotional overtones, one should say I shall, we shall, but you/he/she/they will; conversely, for emphasis, willfulness, or insistence, one should say I/we will, but you/he/she/they shall.
—John Wallis, Grammatica Linguae Anglicanae (1653)
Thus in the quotation from the Book of Job, ke mi povu respondi means "so that I would be able to answer", and the use of povu instead of just povus implies that it is a desire: Job would like to make an answer.