What is the Best way to get to zugspitze summit from Munich?

Yanfen295 -The way I always recommend is that you take the train from Munich to Garmisch. Go downstairs and follow the tunnel to the Zugsptizebahn and catch the train there. You'll change trains in Grainau for the cog wheel train and continue up to the Zugspitzeplatt. From there, you take the cable car up to the peak. Once you're ready to descend, come down using the cable car down to the Eibsee, with incredible views over the Eibsee, ringed by forest. At the bottom, take a walk around the Eibsee (about 1h), and/or have a bite to eat at the hotel restaurant next to the lake. Then catch the Eibsee bus back to Garmisch. If you have the time, get off the bus at the Marienplatz and walk through the pretty pedestrian path through town to the train station, about 15 minutes.

https://zugspitze.de/en/summer/preise/zugspitze

it makes more sense to buy tickets on the spot and check the weather first. Tickets for the cogwheel train can't sell out.

I had read somewhere i can get a train from Munich Centra train station to Garmisch-Partenkirchen .

Yes, and travel on a "Werdenfels Ticket" (available online or from a vening machine), which is cheaper than a Bayern Ticket and not subject to the 9am rule. So you can start early, which you should do even if weather perfect. Clouds are coming up often in the afternoon.

No need to buy the tickets in advance. I would stress that neither the Bayern Ticket nor the Werdenfels Ticket cover the Zugspitz rack railway.