Cleaning up Ngons

 To strictly find ngons: 

Edit Mesh→ Clean up (option box)

Click faces with more than 4 sides

TIPS:

-If the model had multiple pieces do mesh cleanup individually so it is easier to find them on the model

-After doing clean up press Ctrl+1 to isolate the faces that are ngons. Generally, you can just target weld to another vertex in that isolated mode. (Press Ctrl+0 to get out of this mode)