Because there are no specifications as to which form is used or if speed is equalized, there are multiple scenarios as to how this could go, but something to address before my analysis:
In the early parts of JoJo, Hamon is the power used to fight vampires and the undead by exploiting their weakness to the sun. However, when against normal people, Hamon does almost nothing. Hamon affecting a normal human to a degree that matters happened three times in the manga, only one of which was combat applicable: The Deep-Pass Overdrive transferring Zeppelis' strength and experience to Jonathan, Caesar mind-controlling that woman (Joseph never does this in the manga, and it's only implied that he can because Joseph and Caesar were equals), and Kars using it to hurt Joseph after he multiplied its power by several thousand times. So in conclusion, Hamon should not be able to bypass Yang's defenses in a way that hurts, as it was described as a tingle at minimum and a burning sensation at worst.
Anyway, onto my analysis:
Volume 1-3 Yang vs Pre-Training Joseph: Joseph is her equal at that point in AP and Speed. While Joseph is much smarter than her, after hitting her enough, her Semblance boosts her power and all it would take is one good hit to set Joseph up to be pummelled into oblivion. While it would be close, I think Yang would eventually win.
Volume 1-3 Yang vs Post-Training Joseph or Part 3 Joseph: Joseph in either form can react at MFTL speeds; Yang can't touch him no matter how hard she tries. Eventually he will wear down her defenses and beat her. Part 3 would be at an even bigger advantage because she can't see Hermit Purple.
Volume 4-5 Yang vs Pre-Training Joseph: Yang is now is much stronger and faster than Joseph. While he is smarter, he can't hurt her. Yang will eventually win.
Volume 4-5 Yang vs Post-Training Joseph or Part 3 Joseph: Yang can't touch him, but Joseph can't hurt her. It would be inconclusive, nobody would win.
TL;DR: Of the six ways this can go, Joseph wins twice, Yang wins twice, and it's inconclusive twice. It's literally a 1/3 chance as to the victor at this point. More specification is needed from OP.