Github - How to find email addresses for most users
You'd like to get in touch with a GitHub user but, e.g., you don't want to post your question as an issue because, e.g., it's not about a specific repository but more generic.
As a result, the problem can be translated in How to find the email address linked to a GitHub account.
Recently, I had this need in order to contact someone with a Docusaurus blog offering a feature that I couldn't find documented on the web. His blog was not on GitHub but other repos well.
Indeed, GitHub provides a.o.t. an option to make the email private in his user settings page.
Using web interface
Such tool exists on the web like https://emailaddress.github.io/. Just copy/paste there and, perhaps, the system will return any used emails associated to this account.
Using parametrized URl
GitHub provides, in his public API, the list of public events of a given user.
You can retrieve the email using the following URL: https://api.github.com/users/xxxxxx/events/public. Just replace xxxxxx by the Github user you wish to retrieve the email.
Based on a last commit
The first thing is, for sure, to go to a public repository maintained by this person and to find a commit, any commit in fact, that he's made.
On the main page of the repo, locate f.i. the last commit ID he's made:
Click on the ID and you'll get a new web page with a URL like f.i. https://github.com/<USERNAME>/<REPONAME>/commit/<LONG_COMMIT_ID>. Edit the URL and just append the .patch suffix to it (so now, the URL should be https://github.com/<USERNAME>/<REPONAME>/commit/<LONG_COMMIT_ID>.patch).
Before the suffix was added, this is what the page looked like:
And once added:
As you can see, the email address associated with the Github account used to send the commit is now displayed.