Hi Shahul,
Can you please check the following
Ensure that you assign your knowledge article in the application areas of the schema (screen shot attached)
If the system needs to auto suggest knowledge article click on the specific categorization assignment block as shown below
You can then scroll below and assign the specific knowledge article(screen shot attached below) to the categorization.
If you catalog category for the schema configurations are with category type C, then the know article assignment block would be below(check next screen shot) however if the same is D then the knowledge article assignment block would be above when you click on more in your service requests incidents problems.
As explained above(attached screen shots)
However ensure that you select the correct categorization entry and then navigate to the knowledge article assignment block and click on auto suggest(as explained above)
Kind Regards
Atul