First of all I do not recommend using FastQuery, because it can be really slow and many people have had problems with it: https://blog.coates.dk/2014/11/19/sitecore-fast-query-syntax-can-kill-your-sql-server-or-website/
But if you still want to use here is the trick:
The field in Sitecore is not Display Name, it is "Display Name".
standard fields are prefixed by "" 2 underlines char.
Your fast query should look like this:
Display Name for my home item is:
I added #field name# because multi word names should be encoded with "#"
I tried fast query in Developer Center and here are the results.
You need to change a bit of your code to have same pattern like my query from Developer Center.