Quartus VHDL Scematic

Note that there is no way to get an editable schematic(the symbol is just a representation of the ports to instantiate the HDL into another schematic.) You can go to Tools -> Netlist Viewers -> RTL Viewer and get an RTL view of your code. It's not editable or re-usable(which makes sense, since the VHDL is your true source), but it's good for getting a visual of what you've written and how Quartus Integrated Synthesis is interpresting it.