The reason for all this is that the root servers are identified by the character '.' (dot, period) All software I'm aware of (other than really down in the weeds dns code) conveniently implies and/or adds the dot for you.
The server hierarchy is actually like this
.
com org net and others
duckduckgo etc
A request of the A record for duckduckgo is actually
dig duckduckgo.com.