Well, that's an improvement 
!
I'll venture a guess that that /usr/share/pritunl/www/ is probably not the correct webroot of those two domains.
From the looks of things, you've just got a default Apache page, which (I think) is located in /var/www/html/ on Debian.
You can try:
certbot certonly --webroot -w /var/www/html -d jackskomputers.xyz -d vpn.jackskomputers.xyz --dry-run
If you can't figure out the right webroot, you can also try:
certbot certonly --apache -d jackskomputers.xyz -d vpn.jackskomputers.xyz --dry-run