Had testicular cancer in left testicular. & testicular removed. yesterday diagnosed hydrocele in right testicular. will it become a testicular cancer?

Different entities: I'm glad the original testicular cancer is history. If you've had a good imaging study and there's no testicular cancer on the right, i would not worry about the hydrocele -- these are extremely common. You're correct to believe that a second primary in the opposite testis is somewhat more common than random chance. Ask your physician about banking sperms. Good luck.