No, it's not possible to find out the exact number of miners for a block.
Bitcoin mining has become complex over the years and the resources required are expensive. It is
difficult for a single miner to mine bitcoins(but yes, it is possible). Usually,
miners join a mining pool where mining is comparatively of a lower
difficulty level(because the work is divided among the miners in the pool).
Most of the mining pools do not ask for miners to register, due to which the miners remain anonymous.
Hence, the exact number of miners mining a block can not be determined.
But theoretically speaking, "if" all the mining pools keep a log of the miners and "if" the count of
single miners be tracked and "if" the count of miners is made public, then the number of
miners can be determined.
But considering all the "if"s, it is not practically possible.