Pixel Location of Sentinel 1 & Sentinel 2 and SRTM

I am processing integration S1, S2 and SRTM, since their pixel grid does not align with each other I am figuring out how to snap with them all into one grid. Before coming with specific reprojection or resampling techniques I want to know which corner of the pixel is representing ground coordinates for each satellite image (S1,S2, SRTM). I have checked the user guide and technical guide but didn’t get the idea yet at the pixel level.