I'm not sure what's the Knowledge check you need, but see if this helps..
First of all, you really must invest a couple of skill points in those skills, even if they are cross-class, because if you don't, you're limited to DCs lower that 10.
That said, here goes:
"Collector of Stories" skill trick (Complete Scoundrel): +5 in Knowledge checks to identify special abilities of creatures
Items:
- TOME OF WORLDLY MEMORY (MiC, p.190) 1500GPs: 3/day, Study book for 1 minute to receive +5 competence in Knowledge check (standard action if you have 5 ranks in the skill)
- BOOK OF ALL KNOWLEDGE (Complete Champion, p. 142) 3000GPs: 1/day can give a +10 insight bonus to a Knowledge check, if studying the book for 2d4 hours. 1d4 if patron god is Boccob.
+ anything that grants you bonus to skill checks (ex.: Stone of good luck)