Divination

Divination encompasses all those magical techniques with the intent to acquire information.
Be it via spell, tool or ritual.

Truth spells and truth potions, the summoning of spirits to gain information or things such as palm reading etc. are divination techniques.

Divination is also about prohibiting people from gaining certain information. Spells for invisibility or wards against scrying etc.
These are the things a Diviner is well versed in.