My Dad shared this with me today (we live in King County - WA):
I asked 3 questions of a high up activist in my district - and got some answers:
How can we volunteer to check 1) that votes are cast by actual US citizens and 2) that the votes cast by actual citizens are actually recorded accurately representing each voter choice (not altered) and 3) that the actual citizen's vote choices actually end up in an accurate count at the top level summary (not diluted or tossed) that determines how our electoral college representative must cast their vote
As to point (1), it's been pointed out that an average citizen has no real way to determine whether any given individual is a citizen. Even prospective employers can have issues (it's fairly common I believe for an employer who has asked for a SSN later to receive information that there is a "question" about the accuracy of the SSN).
As to point (2), the King County GOP always asks for volunteers to observe the vote count. I've done it a few times myself. I'm not familiar with how that's set up this year, but the office should be able to help. I think there's training involved, although that may be only for the people who do the actual counting.
Point (3) may be more of a computer issue, but from what I've observed once there is a tally for a set of ballots from one or more machine counts, I believe that the number is presented so everyone can write it down, so the manual arithmetic can be checked against the county computer addition. But I may be remembering from one of the challenged recounts.