Scenario : there is a listA in SiteA and another list called ListB in SiteB
In ListA, you are going to add a new lookup coulmn to ListB
by the below steps you can add a lookup column to a list in another Site:
- Navigate to a top level site (which contains both SiteA and SiteB sub sites). If SiteB is the parent site of SiteA, then you can do the following in SiteB.
- Go to Site Settings> Under the Web Designer Galleries, click on Site Columns
- Click on Create link
- Enter a name; Select hookup Field; Enter/Select a Category; Select the list and Column and Save it.
- In your list, go to Site Settings > Click on Add from existing site column
- Select the category and the Site Column you have created > Add
You added a lookup column from a list in another site to your list.
Hope it helps,