I assume you mean the PTO stub shaft out of the tractor will not spin in any of the gears after you put in into the higher speed position.
If that assumption is incorrect then please describe in more detail of what “no PTO” means.
Try to locate a service manual (Work Shop Manual) at Kubotabooks dot com.
I would guess that the shifting forks are not being moved properly. There is a top cover on the transmission that can be removed to investigate, but it carries the shifter mechanism with it during removal (can’t remember if both shifters are are in one cover but think they are). You will need to understand how to get everything back in place when replacing the cover. You can manually shift the PTO when the cover is removed to make sure that it works properly and see if you can locate the problem with the shifter mechanism.
I imagine that the PTO (and drive gears) have to be in a certain gear (neutral?) to put the cover back together properly.
Good Luck.