Barack Obama lied more than once knowing about Hillary Clintons personal server. He not only knew, he communicated with her on it, using a pseudonym.
In March 2015, when the Clinton email scandal was first breaking, CBS White House correspondent Bill Plante asked Obama about his knowledge of the matter:
Plante: Mr. President, when did you first learn that Hillary Clinton used an email system outside the U.S. government for official business while she was secretary of state?
Obama: The same time everybody else learned it through news reports.
Sean Davis, at The Federalist, saw the footnotes showing Obamas involvement.
FBI analysts and Prosecutor 2 told us that former President Barack Obama was one of the 13 individuals with whom Clinton had direct contact using her clintonemail.com account, the report says in a footnote on page 89. Obama, like other high-level government officials, used a pseudonym for his username on his official government email account.