My slave MCU is STM32G0B1 and for master Im going to use SOM which has 3 SPI interface.

 

You connect the devices in such a way that one device generates a signal, and the other device receives the signal. There is only one way to do this.

 

My slave MCU is STM32G0B1 and for master Im going to use SOM which has 3 SPI interface.

By 3 do you mean 3 wire (one wire bi-directional) interface vs 4 wire SPI interface?

One master to the slave in the standard SPI connection scheme for 4 or 3 wire connections. For slave initiated communication/transactions, I use a interrupt line on the master that the slave can trigger by a slave gpio pin toggle to start a SPI exchange from master to slave to receive the slave datastream.