Germ-cell mutations occur in which cells?

The definition of a germ cell is a cell in the gonads,
(ovaries or testes) that gives rise to a gamete, egg or sperm cell. The process of
gametogenesis is where a diploid cell in the gonads, testes or ovaries undergoes
meiosis and this results in haploid cells, known as sperms or eggs, after
differentiation. However, gametes usually aren't capable of surviving for long if
fertilization doesn't occur. Also, spermatogenesis is a more rapid process and
oogenesis(egg production) usually takes longer and is interrupted for periods of time.
Therefore, the answer to your question is germ cell mutations occur in the ovaries or
testes because germ cells are in the gonads and affect the sperm and ova or egg
cells.