More correctly, this sentences would be written "Is what's-his-name still working there?
"What's-his-name" is short for "What is his name", and is used when the speaker can't remember someone's name. (If the person whose name is forgotten is female, it becomes "What's-her-name".)
Normally both people involved in the conversation know the person being spoken about. Sometimes it is followed by a description, to help the person you are speaking to figure out who you mean.
"Is what's-his-name, the man with the red hair and freckles, still working there?"