I translated this as 'my job is near my uncle' and got another correct solution of "My workplace is near my uncle's." So, if I want to clarify in Norwegian that I mean 'near my uncle's workplace' instead of just 'near my uncle', could I say "jobben min er nær onkelen min sin"/"min onkel sin"? Or how else?
You're right, "jobben min er nær onkelen min sin" is a correct translation for that. The Norwegian sentence above would most likely be interpreted as your workplace being near your uncle's home.