The picture book （that I'm reading） was given by jim.{就括号部分提问}
问题描述：
The picture book （that I'm reading） was given by jim.{就括号部分提问}
答
that I'm reading,做定语来修饰the picture book,说明哪本书,或什么书,有特指.所以答案为:
Which picture book was given by Jim?