Does anyone know what 99's name was on "Get Smart?" I don't mean Barbara Feldon, I mean like 86 is Max Smart, so it's her name on the show?

Her name was never revealed. In one episode, where she was leaving control, she said her name was 'Susan Hilton, but at the end, she said that it wasn't her real name.

"Get Smart" never revealed Agent 99's real name. In one episode, her name was given as Susan Hilton, but it was just an alias. The show's producers insist that 99 never had a name in the first place.

http://getsmart.wikia.com/wiki/Agent_99

she said her name was Susan but later said it was not true ,actually she was never given a name by the writers

Agent 99 - A tall, attractive female agent whose appearance becomes useful in many undercover operations. Generally Agent 99 is more competent than Maxwell Smart, but Max saves her life in several episodes. Together they provide a perfect team both to battle KAOS and provide comical situations on-screen. Smart and 99 are married in Season 4 and have twins in Season 5. Agent 99's real name is never revealed. In the episode "99 Loses CONTROL", she says that her name is Susan Hilton, but at the end of the episode she tells Max that in fact "Susan" isn't her real name. In the episode "A Man Called Smart", Max calls 99 "Ernestine". She replies, "That's the first time you've called me Ernestine...If only it was my name!"

https://en.wikipedia.org/wiki/Get_smart#Characters