How to split a stack of consumable items

According to the pillars of eternity wiki, wizards can learn new spells by leveling up or by reading looted enemy grimoires and paying a research cost.

The original source is a forum post by Josh Sawyer:

Outside of combat, wizards can outfit their grimoires with any spells that they have learned. If they come across a spell in an enemy's grimoire, they can choose to learn that spell for the cost (in copper pieces) required to research it.

I have not yet encountered any enemy grimoires in game to test this.

You need to be in scouting mode to detect traps (Alt, or click on the third icon from the left in the bottom row). As far as I understand you also need to have a character with sufficient mechanics skill to detect the specific trap.

Once you detected the trap, select a character with sufficient mechanics skill and just click on the trap to disarm it.