XRT Single Shot Spectrometer - XPP@LCLS - SLAC Confluence (stanford.edu)
go to LCLS tab in mfxhome
click on "XRT Spectrometer"
open a camViewer and open "fee_spec" and look for signal
check the google sheet in that link to find coordinates appropriate for your wavelength.
you might have to tweak position
make sure it is in your data stream if you want it saved.