That’s a very broad question 

Answering depends on how much time you have on your holiday, when you’re planning your trip and what you want to visit.

Take a map, and do some research where you would like to go.

Best use www.bahn.com for your train travel planning to get an indication of the connection and how much time it’ll take you. If you’re looking for dates next your, no single timetable will be available. Than just pick a random date somewhere next week to get an indication.

Well, when you said...it makes sense. Well i was going to be attending a training in Italy in june...after that i would like to cover Munich, Berlin and Hamburg in Germany, Paris, Nice and Marseille in France, Zurich, Bern and Lucern in Switzerland, Monte Carlo in Monaco, Barcelona, Valencia and Madrid in Spain, Lisbon in Portugal, Vienna in Austria, Brussels in Belgium, Copenhagen in Denmark and Stockholm in Sweden.

For the others not in Schengen its Dublin and Cork in Ireland, London and Manchester in the UK.

No particular order but probably theyre all the cities i wanna visit from 1st July to around 19th August...if times on my side i could use 1st july til 1st October 

There are thousands of cities you can visit in EU using your pass - probably 1,000 alone in France or Italy. And UK and some of the former Yugoslavian new countries are not in Schengen but you can still travel to them - in fact, there is an advantage if you are an American - because days in those counties do not count toward your 90 day limit of staying in the shengen region. I met some Australian backpackers in Slovenia who had been traveling 5 months in Europe by using this trick to pop in and out of Schengen. 

That is not true. Americans, and also Australian and other non Schengen/EU nationals, can only stay in Schengen for 90 days within a 180 day period. 

That's not what I said. There are parts of Europe like UK and some former Yugoslavian countries and Turkey which are not part of Schengen. So you can spend an indefinite amount of time in Europe by spending only 90 days total in Schengen region, and the remainder in non-schengen areas. By going back and forth, you can extend the clock. It's legal and does not violate any laws. 

Well you still can't stay longer than 90 days during the 180 days period in the Schengen area. 

Going to Bosnia or Serbia doesn't "reset" your time there aka you can't decide to go to Belgrade for 2 days and then travel for another 90 days across Schengen.