I have a question. I plan to boost a new character to 100 lvl.
I would like to miss the initial training and I know that it can be done. However, will I be able to perform the Broken Shore scenario later?
When you skip it you get told there's some guy you can talk to to do it later. I'd just like to point out though, that if it's your first character, or the first of that faction, you can't skip it
Use your hearthstone to return to your faction's major capital.
There is an NPC (he's by the docks in Stormwind, and outside the front gate in Org) who will let you skip the Broken Shore quest. He will immediately teleport you to New Dalaran.
I do not believe there is a way to experience the Broken Shore scenario if you skipped it. The easy way to experience that content would be to just roll up a new trial character. Play through the quests, then delete him when you are done