A: Richard has been working as a chef at this restaurant for almost 10 years.

B: Where did he cut his teeth for this job?

Note: It’s a metaphoric reference to when a baby’s teeth first appear. Once the baby has “cut its teeth,” it’s properly equipped for the all-important “real-world” task of chewing solid food (metaphorically, for tackling more complex problems in professional life, etc.).

If you say that someone cut their teeth doing a particular thing, at a particular time, or in a particular place, you mean that that is how, when, or where they began their career and learned some of their skills.