Student or Learner
Is it okay to say, "The man have a problem that he cannot retain his memory for any longer than 2 hours"?
As I wrote below, I think the use of "a noun + that clause" is common in English.
The fact that Africa isn't a nation surprised the former US predident.
There was no evidence that he murdered his best friend.
I'm not sure if this use is also applicable to "a problem that...".
May I add?
I think perhaps "The man has a problem, in that he cannot..." might be a little better. I've made bold "has": by saying "in that" you specify both the possession and the problem simultaneously.
Note the subtle difference:
The man's problem, that he cannot retain his memory for any longer than two hours, has caused him great inconvenience. <-- here you are describing the problem directly. (adjective)
The man's problem has grown, in that he cannot retain his memory for any longer than two hours. <-- here, perhaps he could remember 4 hours before; so you are describing how the problem has grown. (adverb)
Or, try, "The man's problem is that he cannot retain his memory...."