Just got a reply from a staff at Shopify and from his response and my tests I understood that you can do things like:
products(first:10, query:"product_type:'Men'")
or
products(first:10, query:"product_type:'Men' title:'My product'")
There has to be no space between the colon and the value queried, and there is no comma between parameters. Also, it’s case insensitive.