An independent clause is a group of words that contains a subject and verb and expresses a complete thought. An independent clause is a sentence.
Jim studied in the Sweet Shop for his chemistry quiz.
The second clause is an independent clause. He is the subject, enjoyed is the action and the book is the object.
The independent clauses are related, so they can be joined to create a complex sentence. They are correctly joined by a semicolon.
A dependent clause is a group of words that contains a subject and verb but does not express a complete thought. A dependent clause cannot be a sentence. Often a dependent clause is marked by a dependent marker word.
When Jim studied in the Sweet Shop for his chemistry quiz . . . (What happened when he studied? The thought is incomplete.)
This is a sentence fragment. We have a "because" but not a "why" or anything accompanying and following what happened "because" they forgot.
Jim is the subject.
"Who likes to read" is a dependent clause that modifies Jim. It contains "likes" which is a verb.
Read is a verb.
A book is the object.