What are every possible 4 digit combinations of the numbers 0 through 9?

There are 10 numbers 0,1,2,3,4,5,6,7,8,9 in all. Case 1: assuming that the numbers can repeat. The first digit can be chosen in 9 ways (exclude 0). The second in 10 ways(include 0) and so...

How many numbers per combination?

Infinite. If numbers can be repeated, the list could go on nonstop.

Too many to list. Allowing leading zeros, there are 5040 such numbers. 4536 without leading zeros.