With this you can get the vector[3] position of where the hit comes from (i.e. end of gun barrel, I assume it should work for knife too and it would look good enough to create the illusion the blood comes from the corpse).
https://www.amxmodx.org/api/amxmodx/get_user_origin
You may take a look at the sprites TE_BLOOD, TE_BLOODSTREAM and TE_BLOODSPRITE (the one you see in HL1 is TE_BLOOD).
https://www.amxmodx.org/api/message_const/__raw
In order to check whether you are around a corpse, you may want to use
https://www.amxmodx.org/api/amxmodx/get_user_aiming and check whether the entity you are looking at has the model of one of your zombie player models.
Or maybe a combination of
https://www.amxmodx.org/api/engine/find_ent_in_sphere and
https://www.amxmodx.org/api/engine/is_in_viewcone if aiming doesn't work.
Either the above or mp_corpsestay 0 and you create your own entities where players die and set some parameters.
__________________