頑張る (ganbaru) is along the lines of "I will do my best" and is a standard word used for things like work and school. ~てみる (verb in the te form and miru) is to "try something and see," like trying to each unagi to see if you like it (食べてみる); it doesn't work for "making an effort to do something."
I'd say どう思いますか (dou omoimasu ka) is fine for "what do you think"
上代 ancient times
城代 chamberlain
perhaps you meant 冗談 joudan, which is joke