I am having this same issue. I am a Virtuoso spellcaster and I know all the spells except the last two Untamed spells. When I try to practice magic, it says I know everything I can for my current level. When I ask the Untamed sage, they say to rank up before they can teach me more.
There are a couple of other thing you can try if you encounter this problem. You can read the tomes for the missing spells, if you have them. Tomes can be bought from one of the stores in the magic realm and they can sometimes be obtained by searching the bookshelves there. Unfortunately both methods are random, so it might take a while to find the specific tomes you need. You can also try dueling for knowledge. I don't use that myself, so I have no idea how well it would work.
The best method is probably the one that @babyzbird suggested. Just Practice Magic in the school that has missing spells.
