How to use " ganbutsusoushi " ??
can i say atashi wa ganbutsusoushi ? or atashi wa aru ganbutsusoushi?
Very streange. Let's say "ganbutsusoushi" is just your nick name because it doesn't have a meaning in Japanese, so you should say "watashi wa ganbutsusoushi"
What he said, the first one. Following the most basic Japanese sentence structure, your second example is impossible; "aru" before the main object can't exist.