As I can see, you didn't read this post "We only give homework help to those who show effort". All I can do is give you advices:
1. About String s: String - is a class, when you create an object of class, the class "do not know about it". So you can't cll the object from the class (String.s = null). Also as in your program.
2. The phrase "data=null" in the begginig of the method is wrong (consider, you use it later...).
3.Befor using variables? you have to declare. That way compiler understands, what you will store in it. In your case the type is "E". this mean, that it unknown now, but will be known later. Also you have to know is the base type for all refference types is Object.
4. If you are writing "public void remove(E data)" it means, that function doesn't return value. The return keyword is not out of place.

Also you can answer a questions and I'll try to answer. Good luck.