I have one specific string, such as \"123abcd\" for example but I don\'t know the name of the table or even the name of the column inside the table on my SQL Server Database
I think you have to options:
Build a dynamic SQL using sys.tables and sys.columns to perform the search (example here).
sys.tables
sys.columns
Use any program that have this function. An example of this is SQL Workbench (free).