Some scientists say a man has a higher chance of having prostate cancer if he doesn'e ejaculate in a regular basis. So, how often does he need to ejaculate in order to stay healthy?

Also can a man ejaculate without having orgasm?

If he does it's not being done right.

I heard the other day that a couple should not go more than two weeks with out having sex, that the case then at least a man should ejaculate at least every two weeks by mean of wife, gf or self pleasure as long as it is done. Clean those pipes.

According to recent medical research, men in their twenties who masturbate at least five times a week have a reduced risk of developing prostate cancer in later life. To answer your second question, it is possible to ejaculate without experiencing an orgasm. Similarly, it is also possible to have an orgasm without ejaculating.

Unfortunately, there doesn't seem to be any surefire way to prevent cancer. However, where the prostate is concerned, the old addage of "use it or lose it" seems to hold true. Many reports have been written that suggest at least 3-5 orgasms with ejaculation per week can help maintain a healthy prostate.

As for ejaculation without orgasm... I think "wet dreams" or nocturnal emissions would be the only normal circumstance.