How many skills can a Duplicant learn before morale runs out?
DuplicantsEasy
Each skill raises the morale a Duplicant expects, and the morale planner checks that need against the rooms and meals you plan. Three digging skills expect 6, while base morale with a Great Hall, a Private Bedroom, a shower and standard meals comes to 15.
What sets a Duplicant's morale need?
Every skill a Duplicant learns raises the morale they expect, and a Duplicant whose morale falls below that expectation takes a Stress penalty. The planner charges one point for a starting skill and one more for each tier above it. Hard Digging costs 1 point, Superhard Digging 2 and Super-Duperhard Digging 3, so the three together expect 6.
The game shows morale against expectation on a Duplicant who already has the skills. The morale planner answers before you assign them. You pick the skills, then the morale sources the colony will offer, and it returns the margin.

Which morale sources pay the most?
Rooms and food carry most of the load. A Mess Hall gives 3 and a Great Hall 4, while a Barracks gives 1 and a Private Bedroom 3. A Standard Meal gives 4, a Good Meal 8 and a Great Meal 12, and a Duplicant who has used a Shower gets 3.
Effects of the same kind replace one another, so a Great Hall does not stack with a Mess Hall and a Private Bedroom does not stack with Barracks. Recreation effects such as Drank Espresso count only while they are active.
When in a colony does morale run short?
A starting skill costs 1 against a base of 1, so Barracks and Standard Meals cover the first skills of every Duplicant. Each later tier costs one point more. Before a Duplicant takes a third-tier skill, plan the rooms or meals that keep the margin above zero.

The planner does not add prerequisites for you, so include every skill the Duplicant holds.