As Gaieus said... it's a rarely used tool, so it is used without a menu item - as explained in the instructions on the download page...
Type
Exportcpoints2csv.new
in the Ruby Console.
You can export any selected cpoints to CSV using this 'Export CSV' tool...
To mark all of the selected Arcs/Circles centers with cpoints, BEFORE you do that final CSV export, you can run this one liner: Copy/Paste the code into the Ruby Console + <enter>
m=Sketchup.active_model;ae=m.active_entities;s=m.selection;as=[];s.each{|e|next unless e.kind_of?(Sketchup;;Edge)and e.curve and e.curve.kind_of?(Sketchup;;ArcCurve);as<<e.curve};as.uniq.each{|ar|ae.add_cpoint(ar.center)}
A cpoint is added to every Arc/Circle's center for you, select them.
The 'Export CSV' tool filters for only cpoints so you don't need to be too carefully making the selection as long as you include the cpoints you want...