How do I find out if my adopted sister is Donald Trump's biological daughter?

So I've seen my sister's birth records and her father was African-American and her mother a white teen of German ancestry. My sister is narcissistic, loves throwing out insults, rowdy, and comes across as a white girl in physical appearance.

My sister has no desire to do the DNA test or contact the birth family despite us knowing the birth mothers name. My parents even met the birth mother and her mother. My sister does not like African-American like the guy who's claim to be her father who my parents have a picture of. He was a teenager just like the birth mother.

So what my question is is this, how can I convince my sister to give me a DNA test so I can find out if she has Donald Trump's daughter? My sister looks too white to be the daughter of the guy photo does the birth father but she's very narcissistic like our president.

Please excuse any spelling errors as I'm talking into my iPhone.

I don't think she's his daughter or you wouldve known by now

For your and especially her sake I hope she isn't.

More challenging for you would be to obtain Donald Trump's DNA!