Using combination of "head" and "tail" to display middle line of the file in Unix

head -2 myownfile | tail -1 

should do what you want

head -2 displays first 2 lines of a file

$ head -2 myownfile.txt
foo
hello world

tail -1 displays last line of a file:

$ head -2 myownfile.txt | tail -1
hello world

I'm a bit late to the party here, but a more flexible way of doing this would be to use awk rather than using head and tail.

Your command would look like this:

awk 'NR==2' myfile.txt

hello world