I don’t think quaternions would be taught in a typical first course of abstract algebra. Do you know of a textbook where they are featured prominently?
I don't know of any book which features them "prominently", but I also don't think you'd really need one. They are taught in various abstract algebra books, they're just taught in the fashion of, "Here's an exercise that introduces a peripheral topic it's useful to know about." For example, groups and rings of quaternions show up in MacLane & Birkhoff's Algebra (62, 426; 282) and Lang's Algebra (9, 545, 723, 758).
Edit: In an effort to find more applied information I put down my math books and picked up the information theoretic ones. You can find more information about the use of quaternions in the two volume Handbook of Digital Signal Processing and Salomon's Data Compression. More generally, when quaternions aren't explicitly referred to it's helpful to look up the coverage of complex rotations, especially with respect to the Discrete Fourier Transform.
I am from Dublin, where quaternions were invented, so they get mentioned a lot by mathematicians and physicists here, maybe getting a higher billing than they do elsewhere. Computer graphics is obviously a place to go for introductions also, but it is typically going to be a more applied and less rigorous treatment.
When I took abstract algebra in Berkeley years ago, they were taught but they weren't the focus of the course. Basically, they're an example of skew field (division ring) so they have some interesting properties that was briefly studied. But obviously, one has to study more to understand their applications.
