If this has been asked before I cannot find it. It is generally accepted that one cannot learn mathematics by purely reading it, the general consensus being that one has to do exercises and as many as possible.
The problem is, what does one do when a book has no exercises? Generally, this is because a book is e.g. more of a monograph, but there are cases where it is really recommended one study a text which has no real exercises. The example that comes to mind most readily is EGA, but past a certain point I’m sure this is the case for most topics.
Usually I guess that is the point where you would be doing research with some guidance from an advisor, but if you don’t then all you have is the text in front of you. What can one do with that?
I would advise researching example problems on the internet, or looking at other similar textbooks that would have example problems. Just read from the textbook, then do problems that have been covered there. If you can't find any problems, ask here, explaining what you covered, and perhaps someone can give you some exercises.