To read the individual harmonic values from the DL850E using SCPI commands, use commands in the Monitor group.
Specifically, use the ":MONitor:ASENd:CHANnel15:SCHannel<x>?" command where <x> is the subchannel number.
The subchannel number corresponds to the harmonic order. Harmonic analysis results are output to the subchannels of channels 15 and 16.