This will do absolutely nothing to your wife's desire except make her coffee distasteful.
Coffee can reduce sperm count but only very slightly.
sperm and eggs
He likes his coffee hot and fresh, just the way he prefers his sperm.
By putting sperm
Yes. As long as there is sperm pregnancy is possible.
Yes
Pregnancy requires that a sperm cell come into contact with an egg. So if the "something" has sperm on, or in it, you can get pregnant. Otherwise, no -- no sperm, no fetus.
Just putting a sperm may not work, as the sperm wil have to go in the vagina and meet the egg.
Yes, it only takes one...
None whatsoever, unless you like a sticky face.
Celery contains androstenone. Eat lots, it's a natural aphrodisiac for attracting women through male sweat and it also boosts sperm production. Another aphrodisiac for women is the smell of almonds (candles etc); also try dark chocolate (make a dessert) and red wine as both contain ingredients which boost women's sex drive instantly.
Take the "morning after" pill. Do not try putting anything in your birth canal to kill the sperm . . . that can be extremely dangerous.