The easiest way would be to use a red command block and a basic green text block -- inside the green text block you would type whatever the npc should say. Then when the mod is run, the text will appear in the minecraft chat area. This would look like the skills and drills < saying hello badge mod. You can use more than one command/text blocks in your mod.
If you want to add an event to trigger the npc's speech, you can do that as well.Maybe a "do _ after _ milliseconds block. Check out the player interact and skills and drills < game events badges to see how to use the event blocks.