First determine which content should be internally and/or externally findable. Not everything needs to be optimised for search engines!
Think of testimonials, for example: the chance that someone will specifically search for a testimonial is very small. It is more likely that someone is looking for information about a certain course, for instance, and therefore enters keywords around the course in search engines. A testimonial is content that can accompany a course. Testimonials are therefore relevant content that the reader is interested in, but not content that is searched for separately. The content is found when searching for an overarching topic. Therefore, there is no need to put a lot of effort into making your testimonial findable by e.g. the name of the person telling the story, or the subject of the testimonial.
That doesn't mean you don't have to think about e.g. a good title, format the headings properly, etc., but you don't have to go through a separate keyword research for this content.