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The Event Horizon Telescope (EHT) is effectively an Earth-sized interferometric mm-band telescope array with 20 microarcsec spatial that is conducting ground-breaking observations of distant supermassive black hole (SMBH) systems resolution. These emission size scales are consistent with those inferred from X-ray and gamma-ray variability thus our request for joint XMM-Newton/NuSTAR /Chandra/EHT observations of a particularly interesting SMBH MKN 501. MKN 501 belongs to a subclass of systems that may consist of a close pair of binary black holes. Along with contemporaneous EHT observations approved for Spring 2019 joint XMM-Newton/NuSTAR study of MKN 501 will provide combined broad-band X-ray spectra and variability while Chandra can provide arcsecond imaging. [truncated! Please see actual data for full text]