Louis Davidson shows how we can find three-part or four-part naming in T-SQL code:
In order to make this work, one of the considerations is to eliminate cross database dependencies, as you can’t reference objects that don’t exist in views, and even in stored procedures, which offer delayed resolution of objects, you can’t test the code without the database it is referencing.
In addition, and somewhat more important to the process, is dealing with three part names that reference the name of the database your object is in. During the comparison process, the database can be created with a name that is different from your target database to compare to (referred to as a shadow database.) So if you are in database X and have references to X.schema.table, but the database is generated as X_Shadow, the X. is now a cross database reference rather than the local reference you are desiring.
Four part names to linked servers are a different sort of nightmare, but one that is (hopefully) exceedingly rare. The queries presented will help with this as well.
Louis has a few scripts to help you find these. If your code is in source control already, you could also build a regular expression to search through it.