It takes time and effort to increase reading comprehension. First, pick a text to read with your child. It should be age appropriate and interesting to the child. If your child is not a reader, pick something that is similar to the child's favorite television show or movie. Check your local book store or favorite book selling website. Many popular children's television shows and movies sometimes have books written to tell other stories with the characters.
Once you have found a book that will work, read it with your child and help them to look for connections to the text so they can practice activating prior knowledge. When good readers read a book, they often find things in the book that will remind them of their own experiences or experiences of others. For example, if you are reading one of the Harry Potter books, you may find yourself remembering how difficult fitting in at school was when you were a child. Making these kind of connections help the reader to understand the book and empathize with the characters, which will then increase reading comprehension. They begin to see themselves in the book and relate to the story.
A lot of times students immediately say that the book doesn't remind them of anything in their lives. Do not settle for that kind of answer! They do not need to find deep and meaningful connections at first. The first ones can be very surface level just to practice. If the only connection your son can find with Harry Potter is that they are both boys, then go with it. Deeper, more thematic connections will come with time and practice as they increase reading comprehension and improve reading speed.
Making a connection with a book is a learned skill for struggling readers. Start slowly. First read books that will be easy to connect with, and then move on to more difficult books that will be interesting and more difficult to read. Over time, the child will find it easier and easier to make connections with a text they must read. Then, instead of seeing words on a page that make no sense, they will begin to see characters and stories that they can relate to and remember.