The testes contributes to about 2-5% of the ejaculate. The main component is sperms which are produced in the seminiferous tubules in the testis. Men who have a reduced volume of ejaculate think they have no sperms. On the contrary their sperm count may be normal.
The bulk of the ejaculate, 60-65% comes from the seminal vesicles which are positioned below the bladder lateral to the vas deferens. The seminal vesicles secrete prostaglandins, proteins and fructose.
The prostate contributes to about 25-30% of the semen volume. The main constituents of prostatic secretion include, prostate specific antigen, proteolytic enzymes and zinc.
These glands contribute to less than 1% of the ejaculate. They secrete mucus and help the sperms swim in the vagina.
Thus we see that all white fluid is not sperm. The seminal plasma contributes to about 95% with sperms being less than 5%. In men where there is no ejaculate, a common cause would be Retrograde ejaculation where all the ejaculate goes into the bladder. A less common cause would be an ejaculatory duct obstruction.