I am not clear on the meaning of the sentence below because of " have only to".
"You /* have only to */ ask him to discover that he hasn't a high opinion of them"
can you explain to me ?
If you omit the word 'only' you'll get the well known phrase which is 'i have to'.
"I have to" means that it is obligatory to do something. In this particular sentence it is "You have to ask him..." which means you must to ask him.