If Kruber can read (which he likely can by now), he learned between V1 and V2. IIRC in V1 there was a Grimoire line (characters in V1 had voicelines when you pulled out grims, and maybe tomes too) where he says something like "Carrying this would be a bad idea, if I could read."
This is actually a mistake. Originally our boy Kruber was penned to be illiterate but this was changed shortly before launch of V1, that line however missed being cut.
Awks.
He's not obviously highly literate but can read as much as someone in his position would be expected to, such as tactical missives