I'm looking for an C.S Lewis quote (where he talks about trees an dryades) which I can citate analogous. Is a question like this on topic here?
Not really. That's more of a literature question really. In fact most SE sites don't handle those sort of questions even when they are topical. The Movies site does, but I'm not sure if Liturature does or not, you could ask on their meta I guess.
We cover a lot of questions about C.S. Lewis's works because he was an influential thinker and writer (if a bit sketchy as a theologian) and so we can cover his theology and it's bearing on modern Christian traditions, but quote requests from his extensive fiction works (even if they do have Christian themes) is not really in our wheel house because they are about his writings not Christianity.
Caleb is right, we don't service Bible ID questions and we don't service Random Christian author questions,
But, I do disagree with him when he writes that fictional works with Christian themes are off-topic. They're off-topic if the theme is tangential to his theology, but since from a certain point of view, which Chesterton (and I think Lewis) held, this is impossible to hold the point of view that anything is truly unrelated from theology, you would have to work to ask a question that is unrelated from Christianity.
I had pretty good success asking about Chesterton here
I don't know how you could phrase this question (I'm not even sure what the question is) to fit on the site.
- What did Lewis say about dryads in relation to trees?
is a bit too broad
- Did Lewis believe in dryads?
is a leading question that might be topical, maybe too specific.
I think fishing with:
- How did C.S. Lewis reconcile a belief in fairyland with Christianity?
and then note in the question that you'd like to know what he thought about different sorts of fairies, dryads being an important one, you may wind up getting what you want out of answers.