Each student has their own textbook. Every student has their own textbook. I think the right one is every student has their own textbook.
Both sentences are correct, but there is a slight difference in their usage.
"Each student has their own textbook" implies that each student has one textbook that is exclusively theirs.
"Every student has their own textbook" has the same meaning but emphasizes that every single student in a group or class has their own textbook.
Both sentences convey the same idea, so either one can be used depending on the specific context or preference.