I think "to wear a pair of jeans" is the correct formal saying but I see many people use "to wear jeans" & "to wear a jeans".
So, to wear a jeans / jeans / a pair of jeans? which one is right?
Jeans is a plural noun like pants/trousers.
So you cannot say I wear a jeans. Instead, you usually say I wear jeans, though you can also say "I wear a pair of jeans".