The small, carved Ivory knife is an angreal aligned to saidar. After Graendal lost her Little Gold Ring angreal during the destruction of Natrin's Barrow, she obtained this new angreal by Mesaana trading it with precious informations.
It is not known how strong this angreal could be, most probably not much, but still enough to step Graendal up over the top male level of strength.
Speculation[]
After the Last Battle and the capture of Graendal/Hessalam it can be assumed that now the ivory knife is in Aviendha's possession.