Hi Ali Yilmaz,
Greetings from Syncfusion support.
We have analyzed your query and we suggest you to get the the filtered column details on Filter Settings from Grid instance when filtering is applied using built-in support. Or if you have used external filter using Query property of Grid to filter records, then we suggest you to get the filtered query details using Query property from Grid instance.
Please refer the attached screen snip for your references
Please get back to us if we misunderstood your query or if you have further queries.
Regards,
Monisha