Real life -> Video game equivalent
You know you need to go to a certain place, You don't know where it is. Others do. -> You can ask NPC's, and then it goes on the map.
You need to find a certain place. You don't know where it is, there's nobody around who does -> You need to look for it. No map pointer.
You don't know where you need to go -> You need to ask around, find clues.
Same with people. If you need to find a certain person, and it would be reasonable for another NPC to have given you a description of what he looks like, then it's OK to have a pointer once he's in line of sight, or a map pointer if your guide told you where to find him. Otherwise, you need to look around or ask others where you can find the person concerned.
And quest givers? If someone has work for a witcher, it's reasonable for them to call out to you, attract your attention, if you get close. But no, no dirty great glowing light over their head.