Depends on their situation and environment. If they have a good manager who recognizes that "helping someone to grow" is better for both sides of the interaction than "drop 'em and take a risk on hiring someone else", and/or if they're in a situation where the engineer can accept the risk that their manager isn't that, it's certainly the best bet.
Employees are an investment. An employee who can take the initiative to flag-up areas that they could benefit from training is valuable.
Comments like these remind that while I miss the US personally, I don't at all miss it professionally. While things in my current country (Norway) err on the side of making it damned near impossible to fire someone, the upside is as a manager I can have very frank conversations with the people on my team about how they're performing. They don't live in any fear of this, they see it as a way to improve.
Employees are an investment. An employee who can take the initiative to flag-up areas that they could benefit from training is valuable.