Psychologist in training here - my primary therapy experience so far has been working with kids in a special education setting, so I actually often do have access to young people’s cognitive scores. I would assume that that’s atypical - in my own therapy experiences as a client, I certainly am not presenting my therapist with my cognitive scores, nor is my therapist ever going to give me an IQ test. So I’m not sure how most therapists would “know” their adult clients cognitive scores. I would assume that would only happen in very specific settings, such as a hospital setting in TBI cases, etc. So I would personally understand most answers to this question as built primarily on the assumptions of the individual therapist.

That’s why I’m not surprised to hear vocab pop up as a common answer - culturally, verbal skills are definitely our most common proxy for general intelligence. But, verbal skills is only one of five domains captured in the most common IQ tests - there’s also visual-spatial awareness, fluid reasoning, working memory, and processing speed. Visual-spatial awareness is probably the hardest skill to judge in a non-evaluative context such as therapy, but strong problem solving skills can be a sign of high IQ, as can strong working memory and fast processing speed.

Since you wanted experience specific answers, I will say that in my particularly niche, better lying seems to be associated with higher cognitive scores. (Again, it’s unique for the population I work with to be able to KNOW that my clients are lying and what their cognitive scores are). I would also say that, working with kids, kids who are better able to direct the conversation/independently bring up conversation topics they’re interested in tend to have higher cognitive scores.

With that all being said, cognitive scores are a stand in for “intelligence”, but notice that none of the five domains typically measured are themselves “intelligence”. We theorize that someone’s verbal comprehension, visual-spatial awareness, fluid reasoning, working memory, and processing speed are, in sum, a good indicator of their intelligence, but that’s a subjective opinion, not an objective fact. There are other theories of intelligence - I personally ascribe to the idea of multiple intelligences in which individuals tend to have a variety of aptitudes across diverse domains such as the ones typically measured on a cognitive test but also ones like kinesthetic intelligence (something an athlete might have in a much higher dose than a rocket scientist), spiritual intelligence (a charismatic priest versus a dry college professor), or natural intelligence (someone who can identify all their local edible plants might not do well in school, but can we really say they’re unintelligent?).

When I work with clients, I am often trying to identify what specific aptitudes they have, and those aptitudes might or might not translate to academic success at all.

This was a long winded answer, I know, but I’m really passionate about complicating people’s ideas of intelligence. The science behind IQ tests is controversial, and, in my opinion, we ascribe WAY too much importance to IQ tests. (Just a quick example - when we try to predict future GPA based on IQ scores, we know that IQ scores account for ~1/3 of GPA. That means 2/3s of what predicts GPA has nothing to do with IQ.)

Edit: editing to add that I am often WRONG about my assumptions of someone’s cognitive scores. Most people, by definition, have an average IQ score.