I am writing about the role of machine learning scientists in developing a solution. Is there a term for the humans who do learning? Can we call a "team of machine learning scientists with their computers working on some ML problem" an intelligent agent? Is "cognizer" the right term? I know that "learner" is reserved for an ML algorithm. I just want a shorter term for their role in cognition, learning.
Is there a term for the humans who do [machine] learning?
Typically you will see "AI researchers" for people studying machine intelligence in general, or "data scientists" for people working with statistics or studying specific solutions in machine learning. Both those terms are used quite flexibly, and generally understood to be scientists/engineers that work on machine intelligence problems. There are also other specialisms that might apply, such as "computer vision researcher".
If you are writing only about researchers who are focused mostly on learning systems - such as new types of learning model, or the best way to train a model for some group of tasks - then "machine learning researchers" or "ML researchers" would be fine. If they are specific people, you may want to ask them directly what title they prefer, in case you accidentally misrepresent their role and work.
Can we call a "team of machine learning scientists with their computers working on some ML problem" an intelligent agent?
No. That might be confused with something that the team is working on or creating. An "intelligent agent" can be the product of specific AI research. For instance, it is reasonable to consider AlphaZero to be an "intelligent agent" (not everyone would call it that, it depends on context, but not relevant to your question).
Is "cognizer" a right term?
No. That is an obscure term meaning something like "a being that perceives or knows". No-one will naturally associate that word with a team of researchers and their computers.
I just want a shorter term for their role in cognition, learning.
I think the most usual way to do this is to describe the team, and name them. For example:
"The MIT computer science researchers are using the X1000 system to investigate learning of abstract spaces. The MIT team said yesterday . . ."
"Professor Hilary Smith is working with a team of graduates on the Learny McLearnface framework. Smith's team have discovered that . . ."
This is the normal way that you see a research team introduced and referred in science journalism in e.g. New Scientist or Scientific American.
If you need to describe some abstract approach about a team working in general, then you can use a similar approach, naming your teams according to how you need to differentiate between them.