What are the opportunites in the military if u join after geting a degree on criminology,law enforcment,or criminal science?

officer

Way back in my day, anyone with a degree had eligibility to enter service two ranks higher, with a subsequent promotion to three ranks higher, than someone without such qualifications. I was even co-assigned with someone in an electronics specialty who had a criminal justice associates but became disenchanted with it as a career. In all likelihood similar fast-track promotions still apply. You may or may not wish to apply your law enforcement training to a comparable military specialty.
You may also qualify for Officers Candidate School should you become interested. See your recruiter.

Of course at the start, you need to pick the degree, but that doesn't necessarily mean that you better actually undergo with it once it has been decided upon

None. Unless you want to be an officer. Otherwise, that piece of paper that you spent four years (or more) getting, is pretty much usless. Anything the military wants you to know about criminology, law enforcement or criminal science, it will teach you.

You'll have an opportunity to get shot at.

No, you better not consider criminology forgoing concluding

Instant Officer...talk to your recruiter. Make a deal. They have to have a need for your profession.