Student or Learner
How would you teach an English as a Second Language student how to use who versus whom?
Welcome to Using English.
They only need to use to use 'whom' after a preposition.
What has your title got to do with anything? Please read the Posting Guidelines, one of which states
'Thread titles should include all or part of the word/phrase being discussed.'
If you had given your thread the title 'Who/whom' the system would have led you to these Similar Threads.
I have moved your thread to "Teaching English" as it is a query about teaching a language point to students, and therefore it's more appropriate here.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.