Do I need to know SQL when I work with Django
You do not have to be a wizard at it but understanding relations between data sets can be extremely helpful especially if you have a complicated data hierarchy. 
Just learn as you go. If you want you can look at the SQL code Django executes for you in the migrations.py file of each app.
I am directing this question to experienced, Django developers, so as in subject, I have been learning Django since September 2016, but I've started to learn it without any knowledge about databases syntax. I know basic concepts and definitions, so I can easily implement in Django models. Summarizing, have I to know SQL to create web apps in Django? Thanks in advance.