Generate the k-ary necklaces of length n
Jelly, 8 bytes

ṗṙJṂȯƲ€Q


A dyadic Link accepting the alphabet size, k, on the left and the necklace length, n, on the right which yields a list of the necklaces using the positive integers up to k as the alphabet.

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How?

ṗṙJṂȯƲ€Q - Link: integer k, integer n
ṗ        - Cartesian power of [1,2,...,k] with n
         -   i.e. all n-length lists using alphabet [1,2,...,k]
     Ʋ€  - last four links as a monad for €ach list, L:
  J      -   range of length - i.e. [1,2,...,n]
 ṙ       -   rotate left by each of those values - i.e. get all rotations
   Ṃ     -   minimum
    ȯ    -   logical OR with L (since the minimum of an empty list is 0 not [])
      Q  - unique values the resulting list