Formal:
* Bakit hindi subukan? (This is the most literal translation.)
* Ano ang masama sa pagsubok? (This means "What's wrong with trying?")
Informal:
* Bakit hindi? Subukan mo! (This means "Why not? Try it!")
* Subukan mo lang! (This means "Just try it!")
More casual:
* Try mo! (This is a simple and direct way to say "Try it!")
* Walang masama sa pagsubok, di ba? (This means "There's no harm in trying, right?")
The best translation depends on the specific situation and the tone you want to convey.