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1. Other damages sustained include a bone contusion and some cartilage damage to my left knee along with a few minor scrapes, none of which were severe enough to even draw blood. (What is 'which' referring to? Is it 'damages sustained' ? For situations like this, how do I know what is 'which' referring to? Is there like a easier way to see it?)

2. The FFS FreeFlow system does improve turbulence and, coupled with the new ventilation systems, keeps the helmet cool and dry at normal riding speeds. (How come 'keeps' is singular? What is it referring to? Is it 'FreeFlow system' ? Again, for situations like this, how do I know what it is referring to ?)

Thanks.
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1. Other damages sustained include a bone contusion and some cartilage damage to my left knee along with a few minor scrapes.

What is 'which' referring to? Is it 'damages sustained' ? For situations like this, how do I know what is 'which' referring to? Is there like a easier way to see it?

{none of which} None of the scrapes were severe enough to even draw blood.

JTT: When you put it in two separate sentences, it is easier to see, Jack.

2. The FFS FreeFlow system does improve turbulence and [coupled with the new ventilation systems], IT keeps the helmet cool and dry at normal riding speeds.

(How come 'keeps' is singular? What is it referring to? Is it 'FreeFlow system' ? Again, for situations like this, how do I know what it is referring to ?)

JTT: Take out the "parenthetical info" and it becomes much clearer.
Comments  
I think that 'coupled with the new ventilation systems' just modifies the subject 'FreeFlow System' which is singular.

What if we edited the text like this:

The FFS FreeFlow system does improve turbulence and with the new ventilation systems keep the helmet cool and dry at normal riding speeds.

Is it correct or it should still be 'keeps'.
 just the truth's reply was promoted to an answer.