Hi Vidit,
Yesterday the "Check your answers" button was missing from the knowledge checks for a while, preventing you from clicking it and completing knowledge check. Please navigate back to the module you were working on and try the knowledge check again.
Below is link to PL-300 course. From there you can complete the module(s) you were working on:
https://learn.microsoft.com/en-us/training/courses/pl-300t00
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP