This was under the assumption that it's a 4 legged dragon. If the theoretical front appendages are arms, no pants up front. Although thinking about it again, with no junk to protect, front pants are kinda useless, so maybe don't bother with them at all.

I'd say for any animal with multiple legs that are very close together, no pants at all would be best. At that point they'd be more of a hindrance than a help!