To copy an exact pose, even if it's between keys, you could: deselect (assuming Lock Dopesheet if off), ctrl + shift + L
for Key Dopesheet (keys all timelines that already have a key), then select the white key in the first row for the current frame, ctrl + C
to copy, ctrl + Z
to Undo the Key Dopesheet, go to another frame, ctrl + V
to paste.