Programmer Evaluation

I asked myself what methods can be used to estimate the level of knowledge and the possible return from the programmer.
I came to the conclusion that the most important indicators are:
- Accumulated knowledge and experience.
- Self-learning.
- The time for searching and finding a solution for the “non-standard problem” (the programmer does not have the knowledge to solve).

The question remains open as to what means to evaluate the last two indicators. If you find a solution to this issue, you can build a more or less adequate certification system on this.