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.