Actually, your question has come up multiple times on this forum and no one size fits all solution has been found.
As far as I understand the 8-direction-behaviour was intended for top-down-view games and therefor has not got this jumping functionality implemented.
Best way I can think of to create stuf like this is having a "Feet-touch-ground"-sprite with the 8 direction behaviour and a seperate sprite with the character/animations..
You could have the feet touch ground sprite to be the shadow of the character..
In normal circumstances the character while being on the ground would follow the feet touch ground sprite and when jumping the two would be seperate..
Giving the character some sort of x and y-vector movement and having it land back on the shadow.