"Do"'s present tense conjugations are:

• I do; we do
• you do; you do (In the Southern dialect of American English, you do; y'all do)
• he does; they do

Thus, "He don't" is not Standard English. It is common in some non-Standard dialects, including the Southern dialect of American English. For example, the song "She don't know she's beautiful."

"He doesn't" is Standard English.

"He doesn't have knowledge about others" sounds odd to my (American) ear. It is grammatically correct, and might even mean what the original poster wants it to mean. Here are some other options that sound more natural to my ear:

• He doesn't know about any others.
• He doesn't have any knowledge about any others.
• He knows nothing about any others.
• That is all he knows.
• He doesn't know anybody else.