You need to contact the website developer who worked on your website since he has that cPanel access. I also suggest that, if you are paying him for the web hosting of your website, you are granted access (he should give you the cPanel login) to cPanel. But if your website is hosted along with the other websites created by this website developer, he cannot give you cPanel access.
In any case, just ask the website developer for the login information of your email address.
Regarding your second question, anywhere you are, with internet connection, you just have to open a web browser, and then go to the link or URL below:
Then you shall be able to login and access your emails.
I hope that helped.
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