Is it a small breed dog? Usually a honking cough indicates a collapsing trachea that your pet needs to be seen for. He could have a number of other conditions, but should be checked out! Good luck!
Welcome to the forum.....It would be impossible to suggest a cough treatment until you have a diagnoses......All cough related diseases are treated differently.....Depends on what's causing the cough.....Good luck at the Vet & please let us know what you find out.....Karla