Doing the following will train this stat (there probably other sources too). Note that ommel materials and the [[holy banana of Oily Orpiv]] are not listed; they have great positive effects on many attributes simultaneously. There are also equipment like [[boots ]] of [[strength]] which increase a stat as long as they are worn.
There are several NPCs, eg. angels, mages, frogs, [[Kaethos]], [[Haathbar]], [[Richel Decos]], etc. which may talk to you about randomized scientific topics if your stats are high enough. This event trains intelligence, wisdom and/or charisma, depending on the talker, but only a few times per one creature.