How to display rows containing special characters in a certain column
Try This:

SELECT F_name  FROM tablename WHERE F_name LIKE '%[^a-Z0-9]%'


What this does is search for 

%.....% : a string
[.....] : that contains any of the mentioned characters 
^       : well actually none of the mentioned characters
a-Z     : from lower-case a through to upper-case Z
0-9     : or any digit


Which results in a search for any character other than a-z, A-Z or 0-9.
Strings that match this would be:

test'user
something?else
I#can#fly


Reference: LIKE (Transact-SQL) (Microsoft | SQL Docs)

After re-reading your question, I would use just: 

SELECT F_name  FROM tablename WHERE F_name LIKE '%[^a-Z]%'


...because you want to retrieve rows with numbers too.