Sorting two columns with sort and uniq

You can extract the first column, pick up the duplicates, and grep them back from the file again:

cut -f1 -d' ' Original_File | sort | uniq -d | grep -wFf- Original_File

The example input and output was updated; the examples in the first section use the original example input to show detail examples on variants:

Original input in Original_File:

User1 US
User1 NG
User2 US
User3 US
User4 US
User5 US

You can skip the userN part for uniq with the option -f to skip leading fields - separated by space:

$ sort -t" " -k1,1 Original_File | uniq -f 1 
User1 NG
User1 US

For the same order as in the example output, you can reverse the sort - this will change the "label" values of the unique lines:

$ sort -r -t" " -k1,1 Original_File | uniq -f 1
User5 US
User1 NG

Note the User5 in the first result line. If that's not acceptable, just sort again:

$ sort -t" " -k1,1 Original_File | uniq -f 1 | sort  -t" " -k1,1 -r
User1 US
User1 NG

If the UserN part is not separated by space, but has a fixed length, you can skip it for uniq with the option -s:

$ sort -t" " -k1,1 Original_File | uniq -s 6
User1 NG
User1 US

With the updated example input, this is the command for creating the required sort order:

$ sort -t" " -k1,1 Original_File | uniq -f 1 | sort -t" " -k1,1  -k2,2r
User1 US
User1 NG
User4 US
User4 EN

it sorts the second field to reverse order.