I guess that depends on what stack you want to use.
You need to know the backend. Pick and choose, really. Python, PHP, Ruby, Java, C#, Go. You need to know databases, relational and NoSQL.
You need to be able to set up a server completely. Depending on what you use for a server (Windows or Linux) this will mean different things. You should be able to set up web server, a mail server, a DNS server, configure firewalls, configure DNS, configure web/mail, write build scripts (Bash, Powershell), use deployment tools (Ansible, Chef).
These days I'd say you should also be able to use a PaaS. Something like Azure or AWS.
And you should be good at all of it.
so if you want to take PHP course here it is:PHP Tutorial | Beginner's Guide to PHP - Edureka
Hope this is helpfull!!
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