You are looking for the method
CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams) in main.cpp.
CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
// Force block reward to zero when right shift is undefined.
if (halvings >= 64)
CAmount nSubsidy = 50 * COIN;
// Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
nSubsidy >>= halvings;
nHeight is the number of blocks that have been found.
consensusParams.nSubsidyHalvingInterval are 210000 blocks, the interval of the halvings
COIN is 10^8, the number of satoshi in one bitcoin
nSubsidy finally gives the number of satoshi that the coinbase may create