Hello,

EdX is one of the free sites that offer many certification programs for students of UG and PG grade. If you wish to pursue courses related to content writing, Edx offers some, but not as lavishly as other sites do. From my opinion, I could say that Coursera offers content writing courses from a basic level to an advanced level. So, if you are trying to earn a certificate for your academics, get in touch with the credit co-ordinator of your department and get to know about the value of Coursera certificate.
For your reference, I have attached links related to content writing:
EdX: (https://www.edx.org/search?q=content+writing)
https://www.edx.org/search?q=content+writing
Coursera:
https://www.coursera.org/search?query=content%20writing&

Choosing the right course depends on your need. Hope it helps.!