Question

We were going to visit my uncle, who/which was working for a technology company in Silicon Valley, before.​

Answer 1

Ответ:

We were going to visit my uncle, who was working for a technology company in Silicon Valley, before.​

Объяснение:

С людьми всегда Who в значении который

Answer 2

Ответ: who

Объяснение: ответ who так как идет речь о человеке (uncle)