What kind of bike rack can go with this bike?
Your bike looks like it comes equipped with a full-suspension frame, and the suspension mechanism is located where one would usually attach the rack stays. This will make attaching a rear rack extremely difficult, and almost certainly less secure. 

I don't recommend attaching a rear rack to this bike, particularly not one that will be holding a child seat. 

Instead, you could look into a child trailer. (For more information on child seats compared to child trailers, have a look at this answer.) Please note that pulling a trailer with any full-suspension bike can cause problems (see the comments).