How a bowler should shoot a single pin spare (ex. 7pin / 4pin / 8pin / 5pin). By throwing a plastic ball straight at the single pin. Or should you throw a strike ball and let it hook to the single pin.

I notice that the pro bowler (male and female) throw a plastic ball at there single pin spares. Is this the “right way” to shoot at a single pin?

THROW PLASTIC, there is less room for error when you throw straight with plastic. You take most of the other factors out of the game that could dictate your shot. For example, lane conditions and oil patterns will determine when and how much a strike ball will hook, it wont affect plastic. Plus with your release, all you have to do is come up the back of the ball. I know there are certain board, arrow formulas people use to convert each pin. The only one I know is for a 10 pin. For RH, stand on 35 and target 20 at the arrows. I have been using that and convert most if not all of my 10 pins now. If I miss one its usually because I missed my mark!! Good Luck
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How am I supposed to knock all 10 down with one ball?!?

Watch the top pros they throw plastic and they throw it straight. If you ever saw the PBA stats these guys are incredible. Walter Ray missed 2 single pin spares in over 400 attemps, and there were other guys that were very close to Walter Ray in that stat.

I use straight plastic to shoot the 6 and 10. Other than that, I use my strike ball for spares. BUT - I have been starting to practice using my spare ball for ALL spares that don't require the ball to move a little. It's tough to make the mental change required to do that, but so far, my percentage on spares is not too bad on the left side. I use a modified 3-6-9 system for my spares, and only miss on the left side if I miss my target.
Now - the right side - that's another story - and MANY, MANY, MANY hours of practice.
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Bowling? Of course it's a sport.