Core concepts to be able to explain
You should be able to explain the working tree, staging area and repository; commits and branch references; merge versus rebase; fetch versus pull; revert versus reset; and local branches versus remote-tracking branches.
Scenario-based knowledge
Instead of memorizing commands in isolation, practice answering situations: How do you undo a published commit? How do you recover a deleted local branch? How do you update a feature branch safely? How do you resolve a merge conflict? How do you avoid exposing a committed secret?
Professional standard
Good Git usage is less about knowing hundreds of commands and more about maintaining understandable history, protecting shared branches, reviewing changes, communicating through commits and pull requests, and choosing reversible operations when possible.