Where is Leonardo's workshop in Venice in Assassin's Creed 2?

Answer 1

In a house.

=P

If you can't seem to find it earlier in the game, wait a while until you unlock the vendors that allow you to travel by carriage (Italy's little taxi service) and there's a preset location directly to his house/courtyard.

Answer 2

Your map actually has an icon for Leonardo (L), you should be able to filter off some of the useless icons to make it a little easier to see where he's hiding.

If you don't find him, try looking at your Uncle's villa (The same room Claudia is sitting in)

Answer 3

If you go to the Map Legend, It shows an icon for Leonardo's Workshop.

The icon is only present if you have a Codex page that needs to be deciphered or need to visit Leonardo to advance the main plot.

Answer 4

He begins in Florence, but will travel to Venice during the storyline, and will go to your villa as well once you've assassinated the last target in Venice.