After discovering the severed head of Rakharo inside a bag carried by Rakharo's horse, Ser Jorah Mormont considers either Khal Pono or Jhaqo as the culprits and that Rakharo was killed as a demonstration of contempt for the notion of a female leading a Khalasar.
In the books
In the A Song of Ice and Fire novels, Pono is a ko in Khal Drogo's khalassar. After Drogo's fall from his horse and subsequent incapacitacion, Pono is one the first of several kos that declares himself Khal, taking ten thousand of the khalasar as his own.
In "A Dance With Dragons", it is reported that Pono is near the headwaters of the Selhoru with a khalasar of thirty thousand, and that other khals fear of him.