The meaning of sub-competence

Usually you would see incompetent, which is a combination of "competere" (think compete, and fitness or match) and "in-" the standard issue negating prefix (e.g., invalid, incomplete, imprecise [the bilabial phoneme comes into play here because of the p]).

I'm no linguist, so I cannot say whether sub-competent has literary precedent. However, from it's composition, I would define it as such:

sub-competent (adj): below or beneath the necessary level of competence.

Which is basically incompetent. The only difference I would suppose would be that incompetent refers to a generally absolute level of inability; i.e., you cannot do it at all; whereas sub-competent would imply that you can do it to some degree, and it may be a skillful level, even, but it is not sufficient to complete the task at hand. I would note that this semantic line is so gray that it may not at this time be linguistically productive to use this term.

sub-competence (noun) =

The roots of this saying are in the French language, 'la sous-compétence'.

The term is often used in the context of pedagogy. It means those skills that are below, being part of, the most important skill.

So, for example, to be able to write, you need to know the alphabet > knowing the alphabet is sub-competence of the competence of writing.