According to different sources it varies. The Transformers version is the most accepted "Bah weep graaagnah wheep, ni ni bong".

The Children of the United Nations use a slightly more energetic greeting, seemingly created by Gong Master Don Conreaux
    1) I / WE OFFER YOU PEACE - Face palms forward, elbows bent.
    2) I / WE OFFER YOU FRIENDSHIP - Cup hands palm to palm, elbows bent.
    3a) I / WE OFFER YOU LOVE - Draw hands forward...
    3b) from the heart...
    3c) to form a cup.
    4) I / WE HEAR YOUR NEEDS - Cup hands behind ears.
    5a) I / WE SEE YOUR BEAUTY - Cover eyes with hands...
    5b) then uncover.
    6a) I / WE FEEL YOUR FEELINGS - Arms across chest...
    6b) fingertips to shoulders.
    7a) ALL WISDOM FLOWS... - Move right hand palm down from overhead...
    7b) past face to meet...
    7c) FROM THE HIGHEST SOURCE - upfacing palm at chest, fingertips forward.
    8) I / WE HONOUR THAT SOURCE IN YOU - Palms together in prayer position.
    9a) LET US WORK TOGETHER - Fingers interlocked...
    9b) as two-handed fist.