The feminine form of the word 'Author' is :

datum (noun - Singular) a piece of information. "The fact is a datum worth taking into account"

-দুইয়ের অধিক  বিষয় বা বস্তুর মধ্যে তুলনা বুঝালে সেক্ষেত্রে Superlative degree বসে। 
-আর Cheap এর Superlative degree হলো Cheapest যার অর্থ সবচেয়ে বেশি সস্তা।
-বাক্যের অর্থঃচারটির মধ্যে লাল বইটির দাম সবচেয়ে কম।

The correct sentence is:
He does not know how to swim
Here is why:
Subject-Verb Agreement: The subject is "He" (third-person singular), so it requires the auxiliary verb "does," not "do." (This makes "He do not know..." incorrect).
Grammar Rule for Skills: When using the verb "know" to describe a skill or ability, it must be followed by "how to" + the verb. (This makes "He does not know to swim" incorrect).