I just killed Lareth and opened his diary. It starts off "You can't seem to find any visible script...".

Nulb does not show on my World Map :confused:

What do I do now?

...visible script? I don't know if that's a game bug, or if your character has insufficient intelligence or what.

But don't despair, you can still get to Nulb. Talk to the jeweler, and he'll have a conversation option that has him tell you how to get to Nulb. There may be others in town who will tell you, but I got the information from the jeweler so I can vouch for his directions.

Or tell Burne and Rufus at the castle about clearing the Moat house, and they'll put Nulb on your map.(plus some XP I think...)

I finaly figured it out. You "use" the diary. Then Nulb shows up on your map.