If I have a follow-up question for someone who - thru Community - has replied to 1 of my questions, then how do I reply to the answer or ask a follow-up Q of him or her?

See above

Troubleshooting

Hi pirateeinuk,

 

You can@mention Community members by their username.  This alerts them and lets them know that someone has responded directly to their message.
(eg. “Loved your suggestion @pirateinuk ")