How many kg of steel reinforcement in one cubic meter concrete?

It all depends on the type and sizes of the steel used. It also depends on the load that the concrete has to take at certain points. 7865kg is the weight of a cubic meter of steel.

Typical examples;

A pile cap could contain 400kg/m3

A heavy duty industrial slab or structure could contain 200kg-400kg/m3

A footpath could contain 40kg/m3

(all depends on the design, but numbers above should give you a rough answer)