Thank you so much. I had a look at in-game settings.. My 'gameinstructor_enable' were set to 0, that's why I can't see the instructor hint. The instructor hint is working normally.
Now I've found out that, hint text that is used by 'bosshp' and 'shop quiz' is not instructor hint,
but the game internal feature itself. 
Thank you for solving my problem.
Updated: I decompiled some maps that are not using BossHP and found out that, you can display the hint message by using "env_hudhint".
Usage:
"env_instructor_hint" -> Pointing out mission's location.
"env_hudhint" -> Display hint text at the bottom of player's screen.