EV Certificate - what's required for validation?

I’ve never been able to find a conclusive answer to this.

What documents do we have to provide to get an EV certificate? Or do we have to provide any documents? Is all of the vetting done on Comodo’s side?

I've never been able to find a conclusive answer to this.

Please check the below articles for some detailed information regarding your query.

https://support.comodo.com/index.php?/Knowledgebase/Article/View/253/0/what-is-required-for-validation
https://support.comodo.com/index.php?/Knowledgebase/Article/View/702/0/ev-certificate-validation-checklist

What documents do we have to provide to get an EV certificate? Or do we have to provide any documents? Is all of the vetting done on Comodo's side?

Most of vetting process is done by COMODO. Sometimes they require you to contact a local vetting agent for some additional or regional level verification.