I was just wondering....

Their ability to spend a fate point to pass certain tests.... does that mean they don't need the particular knowledge skill in question then, or would that still be required? Just that the idea of having my Seneschal player spend a fate point to go "Oh yea, I remember reading that somewhere" sounds kinda like how I'd expect it to work, but I just wanted to check.

To make a Test on an Advanced Skill, you need the Skill in question, so no. However, once they get Infused Knowledge, all Lore skills become Basic Skills, so at that point they could use the ability for any Lore test.