jQuery Migrate is the more common of the two in our index: it runs on 5,087 websites against 183 for ScrollMagic, and 41 sites use both. Counts come from real scans, not vendor claims.
Query Migrate is a javascript library that allows you to preserve the compatibility of your jQuery code developed for versions of jQuery older than 1.9.
ScrollMagic is a jQuery plugin which essentially lets you use the scrollbar like a playback scrub control.
41 sites run both jQuery Migrate and ScrollMagic. That is 22% of the sites using ScrollMagic, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.