Law-school examinations have not changed all that much since you were a law student. Essay exams predominate, but some faculty are using multiple-choice questions as part or all of their tests. Other choices you will have to make include closed-book vs. open-book and scheduled vs. take-home. Each choice has advantages and draw-backs. One or more of these options may be prohibited or frowned upon by your school, so this is another area in which the academic dean (as well as full-time faculty at your school) may provide helpful guidance.
The Jurist website has a page devoted to law school exams. The page is intended for test-takers, not those who write them, but there is some food for thought for law professors as well as law students. If you decide to follow this route, consider reading what the students are buying to guide their test-taking, e.g.:
Check out the "exam bank."
Saint Louis University maintains an exam bank for various health-law-related courses around the country. For access to the exam bank, send an email to Professor Sidney Watson.
Grading exams and determining final grades can be challenging for full-time faculty, who at least have the advantage of frequent repetition. Adjunct faculty need to be aware of their school's policies, which may be quite detailed. The absence of a detailed policy, however, is not an indication of this subject's importance. The registrar's office probably has data or reports that describe the average, high/low, and and grade distributions for large, medium, and small classes, seminars, and skills courses.