How to fix "not enough educated workers" building issue? Make sure you have elementary school, high school and university service buildings. Note that you cannot just plug in university and immediately expect this issue to be resolved, it will take a long time for students to graduate from the whole education system (elementary, high and university).
Commercial, industrial and office buildings need workers with different education levels. You need elementary, high school and university schools.
Lack of public transportation or traffic jams could cause this as well.
Generic industrial buildings (before "leveling up") require a lot of uneducated workers. Low density commercial buildings also prefer uneducated workers but they start to require a bit more educated workers too.
High density commercial buildings require kind of medium level educated workers, "educated" and "well educated" workers.
Office buildings require... well lets be honest, only HIGHLY educated workers. If you haven't grown your population with university schooling don't bother zoning offices because the buildings get "no enough educated workers" icons floating above them immediately.