There is no definitive confirmation that Hitler had Jewish ancestry but this is one of the most frequently asked questions about Hitler himself.

Historians such as John Toland have examined stories which suggested that Hitler's father, Alois Hitler, may have been the son of a Jewish father. Alois was registered as an illegitimate child when he was born in 1837 and to this day the identity of his father is unknown. His mother had worked in the home of a wealthy Jewish family and it has been suggested that there is a small and remote possibility that a son in that household had gotten Hitler's grandmother pregnant.

Studies have been done to try and use DNA to identify if Hitler had any Jewish ancestry. Saliva samples were collected from 39 relatives of Hitler which found some commonality with chromosomes found in Jewish groups but all in all the study was inconclusive. The rumours of Hitler's ancestry are enough that it has become one of the most well known historic myths of the Nazi era; it is widely accepted in historiography of Hitler that he did not have any close Jewish ancestry and it is now often dismissed as a 'conspiracy theory' due to the lack of compelling evidence.

Here are some links to articles which cover the topic and the studies that have been done:

https://www.jewishvirtuallibrary.org/was-hitler-jewish

https://m.huffpost.com/us/entry/us_693568

https://www.timesofisrael.com/historians-cast-doubt-on-hitler-jewish-heritage-claims/