There are no international trains in that area: either due to year-long engineering works or political tensions (often the latter).

There are also no railways along the coast.

Buses are running but they're not included/no discount. Tickets are cheap anyway.

You could get to Belgrade by bus and then take the daily night train to Bar (Montenegro). Reservations only possible at Belgrade train station so be a little flexible.

Scenery is stunning early in the morning.

Then Bar - Dubrovnik - Split by bus before you meet rails again.

Is there an easier wat to go to split from north Macedonia? 

Avoiding the Belgrade - Bar train would be the easiest. From a quick look there's an overnight bus from Skopje to Zagreb, then take another bus or one of the rather infrequent trains.

Since the train ticket costs 15€ it doesn't make sense to use a travel day.

Oke thank you. Do you have the links to look at the timetable and to book the busses and trains. 

Nope. I had a quick look at Flixbus but there are dozen other companies which don't have websites.

Go to the bus station in Skopje and ask. Have cash in case.

rome2rio.com often has bus timetables in this part of the world, though not necessarily a definitive list.

Also try getbybus.com, busticket4.me

Sometimes asking at the bus station is the surest way to find out!