Update: some people have mentioned the tracker is buggy and remains at 98% for awhile but it does seem to unlock when you have all 99 skills
This will probably be the last achievement you need and if so the best way to farm for cubits is by running Joblin repeatedly.
You should have Tappi as your mentor and cubicle rewards member as your pinned skill. Tappi gives you extra cash and allows cafe items to restock. This means if you buy the cubits bundle in the store another one will pop up meaning you can pick up a fair few.
Also Joplin is the easiest to complete and get the cubit bonus crate at the end. Just grab a tablet pen and wail on the boss . The electric shock stuns him and he can't attack. There are usually some in the boss room too.
I should also add make sure you've turned on all the assists as these do not affect cheevs
I was getting 200+ cubits a run this way