If the former, I suggest digging into things like the excellent Fast AI course: https://course.fast.ai/
If the latter, the (relatively new) keyword you are looking for is likely "AI Engineer" - https://www.latent.space/p/ai-engineer
There's an argument that deep knowledge of how to train models isn't actually that useful when working with generative AI (LLMs etc) - knowing how to train or fine-tune a new model is less useful that developing knowledge of the other weird things you have to figure out about prompting, evals and using these models to build production-quality apps.