High-redshift quasars can shed light on the co-evolution of central supermassive black holes and their host galaxies in the very early universe. Observational constraints on radio jet and interstellar medium feedback processes are still very limited at redshifts z>2. We investigate the radio-loud quasar P352-15 near the end of Reionization at redshift z~6. This quasar is the most powerful radio emitter with direct evidence of a kpc-scale radio jet (~1.6 kpc) at these high redshifts. I will present the results on the spectral energy distribution of this quasar at millimeter (far-infrared in the rest-frame) and radio observations. The millimeter continuum emission for radio-quiet quasars at these redshifts has usually been interpreted as cold dust and is modeled as a modified black body. However, the analysis on this radio-loud quasar shows that it is not possible to model the millimeter measurements as cold dust alone. I will present evidence of the strong radio synchrotron emission in this source affecting the dust-dominated continuum emission in the millimeter, and implying a break in the synchrotron spectrum. I will further portray the big picture in a dedicated study for the first time on measuring different jet lifetimes based on rest-UV/Optical and radio observations of this quasar. Thus, constraining the black hole - host galaxy formation and jet ejection mechanisms of a quasar in the first Gyr of the universe.