How do gymnosperm leaves differ from angiosperm leaves?

I think there may be some confusion on the question. The terms Gymnosperm and Angiosperm don't have much to do with leafs. It is more about the seed structure than leaf structure. However there are some basic generalizations about structure that can be made.

• Gymnosperms are a class that includes plants whose seeds are not enclosed in an ovule (like a pine cone). Gymnosperm means as "naked seed".

• Angiosperms are a class of plants in which the mature seed is surrounded by the ovule (think of an apple).

Your question is very broad we can not talk in absolutes in biology however i can give you some general info:

Generalizations about leaf structure

• Gymnosperms usually have needles that stay green throughout the year. Examples are pines, cedars, spruces and firs.

• Angiosperms usually are trees that have broad leaves that change color and die every autumn. Oaks, maples and dogwoods are examples of deciduous trees. Some angiosperms that hold their leaves include rhododendron, live oak, and sweetbay magnolia.

I think this questions is actually asking what is the difference between deciduous trees and evergreen leaves. here is a quick rundown