After viewing logs with journalctl, how do I exit the screen that says "lines 1-2/2 (END)"?

A smooth way to end that command is to hit q (for quit). It looks like it is viewed with the viewer less.

You can quit from this command and several other text mode programs with q. In this case and several other cases you can also quit with the ctrl C interrupt, but it is 'more brutal'.

Read man journalctl. In the Description section, it says:

The output is paged through less by default, and long lines are "truncated" to screen width. The hidden part can be viewed by using the left-arrow and right-arrow keys. Paging can be disabled; see the --no-pager option and the "Environment" section below.

So, you should read man less to learn about this useful tool.

One of the things you can learn from man less is:

   q or Q or :q or :Q or ZZ
          Exits less.