You need an article or determiner and a sentence that matches your perspective and the context or situation. 1 get onto the motorcycle if you know the motorcycle. 2. get on this motorcycle, the motorcycle in question being pointed at. 3. get on the motorcycle = same as 1 can use on or onto. 4. get on my motorcycle 5 get on his / her / their motorcycle. 6 get on a motorcycle, if you are suggesting someone takes a motorcycle trip/ ride 7 get on your motorcycle, feeling someone to get onto their motorcycle 8 get on that motorcycle the motorcycle you are pointing at 9 get on John's motorcycle, the name of a person who owns or is using the motorcycle 10 get up on can use with all of the above. You can also say get aboard jump aboard climb aboard the possibilities are Endless and UK British English tends to use motorbike more commonly and we also know and use motorcycle

As Simon demonstrated, you need an article or some other determiner since it's a singular countable noun. In American English, we would always say "get on a motorcycle." It would sound weird to use "get onto."

Get on/onto a motor cycle