I'm sorry that i can't help you, but i was wondering the same, so thank you for asking. I'll follow this post.
It's not human readable.
If you want to code use the sdk: https://www.scirra.com/manual/15/sdk
When you export, the code for your game is in the js files that are exported. It's not readable though.
Edit: now that I read the previous reply again I find myself pretty redundant. Guess I should sleep more.
You can Export it with something like HTML5 Website (I know You can see all the JS code by that), but, anything other than that is beyond any of our help.
Develop games in your browser. Powerful, performant & highly capable.
If you don't use 'minify' then the HTML5 export is readable. Whether it is understandable is another matter.