What does ‘Reserving judgments is a matter of infinite hope. I am still a little afraid of missing something if I forget that, as my father snobbishly suggested, and I snobbishly repeat, a sense of the fundamental decencies is parcelled out unequally at birth.’ mean?

See a translation

Of course haha

In English, when you say
나 아는 사람
the "는" translates like "that"
So it will read like "The person 'that' I know"

And when you say
그거 얼마에요?
The "그(거)" translates like "that" as well
So it will read like "How much is that?"

Actually, I think this passage is very difficult, even for an English native ^^'
If you take out the useless words, this is the full sentence:

"I am still a little afraid of missing something if I forget that a sense of the fundamental decencies is parcelled out unequally at birth."

If you break it up like a Korean sentence, it will look a little like this:

(a sense of the fundamental decencies is parcelled out unequally at birth.)를 잊는다라는 무언가를 잃어버리"는 것이" 조금 무섭다.

So the "는 것이" here means "that"

이게 도움 됐어요? ^^