I want to check if a request for the same person (and other conditions...) is exist in other list of the form.
The problem is that every user can see one list, but just few have permission for the list I need to check.
Therefore, the lookup is not return weather or not the item exist.
How can I make the lookup happen from another user - like in the WF?
Have you tried placing the lookup in an Action Set and configuring it to "Run as workflow owner"?