One thing one needs to be aware of is that the human sense of smell is usually acutely underdeveloped while the actual sensor is fully functional and, while not on par with that of a blood hound, capable to a lot more than what modern life ever asks of it. Some forms of color blindness work similarly.
As a result, individuals' sensitivity to smell signals varies wildly. Now the remaining reliable areas of significant body hair coverage (axle and crotch hair) have been kept around by evolution for distance-signalling of the availability of mating partners. This is achieved by different sweat glands in that area cultivating a bacterial lawn of their own.
This is quite natural. Also quite undesirable in the confined spaces of modern life. I have a pretty solid sense of smell (I can distinguish most horses on our grounds if you towel them off thoroughly and let me smell the towels but again: horses are intended to have individual smell), and I had to give up on thinking that showering thoroughly and changing into fresh clothes was enough to get body odour under control sufficiently for not distracting/annoying me. I had to revert to hair removal at least with regard to the axle hair in order to get rid of the bacterial reservoirs readily providing bad smell pretty much right after showering with the first trace of sweat.
Now that's all anecdotal and whatever but the point is that body odour might not be accessible to measures that are even remotely suitable for suggesting to a colleague. Regular hygiene and change of clothes can be expected when a problem has been brought to notice. But it is not guaranteed to do the job, at least not for everybody in smelling range.
There is the additional problem of not just the "smelly" areas: skin has its own odour, partly determined by the sweat from the "non-stinky" glands. That of smokers smells rather pungently, people eating a whole lot of garlic smell strongly. And people of different race to your own have a different odour that is more distinctly noticeable than that of bodies more similar to your own.
Modern life is not organized in tribes, so you cannot afford getting distracted by the uncontrollable biological tribe markers, and bringing them to attention would be seriously unfair and offensive.
Which may explain the overall taboo on discussing all smelly things. Some people just cannot do a lot, and some people likely could.
After all that, there is not a lot to recommend in consequence that hasn't been said by others: don't be an ass about this. If this is going to end up a serious impediment for the person's employment, you have to give him the chance of changing it. There are a lot of reasons the person might not be aware of how much in excess of "standards" his/her smell is. If the person is lucky, he still has enough of an own sense of smell to assess his own impact on others once he has readjusted his attention. Otherwise he might be in the situation of a blind person applying makeup, finding someone in his personal circle who can, once asked, provide the necessary feedback until routine sets in.
The "worst" that can happen is that he drops out of one job out of embarrassment for having made a bad olfactory impression. Still better than getting shunned or let go again and again without having a clue why.
And to give this some perspective: the one colleague where I'd really have had a terrible time of sharing a room with him went overboard the other direction. I could tell whether he was on the floor when I arrived due to his choice of body care products. He went out of the country in between (incidentally, to the U.S.) and some months afterwards I enquired from a colleague whether he was already back ("what? No, he's away for half a year."). Later that day I saw him (he was on vacation) and he apparently had been in briefly before I had arrived.
When he finally returned, he was inconspicuous. Either somebody had clued him in, or he had run out of his usual product or whatever. Now that was for somebody who smelled "too good" and yet I never brought myself to tell him.
I hope you do better than I did.