This isn't really a matter of where you've been, but rather how far you have been. The question is how far you've traveled from home going in all four cardinal directions; North, South, East, and West. You can include intermediate directions like Northwest if you feel like.
Also include where you live if you don't mind (you can write the continent if you really don't want to tell us! :comeatus: ).
You can include where you've visited (spent a decent amount of time at) and include where you've been (i.e., an airport for your connecting flight).
For myself, living in Austin, Texas:
North: Frankfurt (airport), Germany; Prague, Czech Republic (to be replaced by Aarhus, Denmark!)
South: Acapulco, Mexico
East: Budapest, Hungary
West: Phoenix, Arizona
Disclaimer: aside from Acapulco, I've been to these places all within the last 4 years (I haven't traveled much). I've traveled very little within the US.
Also, if you have traveled far enough West that you passed your farthest East point by a small bit (unlikely but possible), you can say you've traveled along every single longitude line, or just indicate up to what point you stopped traveling in that direction.
You can use this map as a reference (you may want another map if you need to zoom in or need a more specific map):