I don't understand. Do you want the sphere jig to turn the outside? The curve of the shape you show doesn't look even close to a sphere on the side (from the view in the photo). If you want the outside of the bottom 1/3rd or so to be spherical it seems the jig should work fine, assuming you get one with the right height to match your lathe. The upper part would have to be done by hand as usual because of the handle.
It looks easy enough to turn without a jig, though, using the method of marking off 8ths and 16ths (or even wimp out and buy the Berger calipers!:
https://sorenberger.co.nz/products/s...sphere-caliper) In fact, I'm wondering if a perfect spherical bottom would be difficult to blend into a pleasant curve on the sides without looking stilted. (None of the pictures I saw for kuksa/guksi/kasa cups looked spherical, all quite flat on the bottom, I assume to sit on the table.)
Or do you want the entire thing to be a sphere instead of the shape shown? Could you not turn the outside in the other orientation, with the handle on the lathe axis towards the spindle, then jam mount 90-deg and turn the inside? This is the way turners sometimes make coffee scoops, sort of like this video but with the wood that will contain the handle initially towards the headstock and held in a chuck to allow using the sphere jig:
https://www.youtube.com/watch?v=jgm9gmtHhNo
Or maybe I just don't understand! Maybe more pics, description?
BTW, beautiful work on the cup in the photo. I love the shape. What kind of wood did you use?
JKJ