Question

How you would encourage him into wear glasses, and *What you would say to convince him.

Answer 1

to convince him to wear glasses, we can use "should" for simple convince and "Ought to" for emphatic convince. , it depends on the situation.

So, the probable ans, is: You should/ought to wear glasses.

[it it's extremely necessary for him to wear glasses, I prefer using "Had better"

You had better [short form "You'd better] wear glasses. ]