Student or Learner
Which one is correct?
1) When did you started this job ?
2) When did you start this job?
Once you have a form of the verb "to do" you leave the other verb as a bare infinitive - that is the "to X" form without the "to."
So "When did you start" is correct.
I know him. Do you know him?
She knew him. Did she know him?