Trello API get card comments
Comments are a type of action ("commentCard"), so look into the /card/:id/actions
Try this API URL
Method: GET
https://api.trello.com/1/cards/{card_Id}/actions?filter=commentCard&key={trellokey}&token={trellotoken}
GET /1/cards/[card id or shortlink]/actions
you'll get list of action-objects in json, each has its type, type for comment "commentCard", comment text in
object.data.text
https://trello.com/docs/api/card/index.html#get-1-cards-card-id-or-shortlink-actions