NR==FNR  -->  While the condition NR==FNR is true, 
NR --> Record Number which counts all the lines in both files, 
FNR --> Filename Record Number, which counts the lines in only one file, then restarts numbering when the lines of the second file are being processed,  then continue with the  other statement:
{a[$2]=$2;next} --> build the array a with all the elements from field 2 of the first file HDBOXREPORT while NR==FNR is true,
next --> read all the elements from that file, without continuing any further in the script.

$7 in a --> Special test operator of assocciative arrays that checks if elements of field 7 ($7) from file QSPK-list are part of the array a created from file QSPK-list. When this condition is true then:

{print $7, $8} --> simply print the required fields from file QSPK-list.