Suppose I am a user of stack exchange chat. And I am on Android mobile. My questions are 1) How do I enable Mathjax In chat. Can I? I am asking as the question asked was answered for computer not for mobile.
The ChatJax bookmarklet appears to be designed for both desktop and mobile browsers, and indeed there's a specific version for "troublesome mobile browsers" to try out if you find it's not working.
As to how you can install a bookmarklet on a mobile browser - that will vary depending on the browser, and it may not be possible on some browsers. Your mileage may vary here, and I'm reluctant to recommend solutions as the different routes may or may not apply depending on individual situations (such as e.g. willingness to sync mobile and desktop bookmarks).
Alternatively, you could install Tampermonkey as an app and then run the ChatJax++ userscript over it, though again that has some significant overheads.
Generally, to the best of my understanding, rather few people in this site's community use MathJax for chat over mobile, given how hard it is to write LaTeX on mobile keyboards so you're mostly doomed to one-sided conversations even if you can see other people's MathJax rendered correctly.