how to calculate the value of strobe signal in axi?
The slave could theoretically check whether the WSTRBs send are legal (i.e. whether they're consistent with AxSIZE, AxADDR), but it couldn't always rely on recalculating it's own WSTRBs for legal combinations. If a master sends a sparse write (e.g. WSTRBs = 0b0101), then there's no way for the slave to reconstruct this using other attributes.
I don't think you would implement these functions exactly as they are described in the Specification, but you would implement equivalent functionality in hardware.
I'm not sure if there are any diagrams of this, but there's someone online AXI training material that is available at https://developer.arm.com/support/training