I just had another student book this time/I just had another student booked this time 哪一句是對的？

If a school teacher service is fully booked, it has no room time-date left for any other engagements.(student booked=has booked--vt.)) is correct.
Or had another student book being kept in a place--To keep a book(noun) in the student's locker..

"I just had another student book this time."
If "book" here is a noun used as an object in a sentence, then "student" should be in possessive (showing ownership) form as in "student's" book. 这句才是對的:
"I just had another student's book this time."

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"I just had another student booked this time."
If you mean "booked" used as a verb, I think it should be in the present perfect tense instead of the past perfect tense and that is "have booked" meaning have registered or have engaged or have reserved..... 这句才是對的: "I have just booked another student this time." or "I just have another student booked this time."
The Past Perfect Tense that is "had+ past participle" is used when something happened in the past before another action happened in the past. Like for example: "I just had another student booked before you arrived."