Exactly what data should be in those 2 columns?
It's fairly easy to write a python script that print data to file:
f = open('file.dat', 'w')
data1 = [1,2,3]
data2 = [4,5,6]
for d1,d2 in zip(data1,data2):
print >> f, d1, d2
f.close()
I suggest you take a look at the documentation for the Bandstructure object to figure out how to retrieve the band struacture data you want before writing it to file: http://docs.quantumwise.com/manuals/Types/Bandstructure/Bandstructure.html (http://docs.quantumwise.com/manuals/Types/Bandstructure/Bandstructure.html)