The most easy method to check if a port blocks for a vlan is the port list in the command "show vlan <vlan>
". If a port is blocking it will show a 'b' behind the port number.
Also checking the protocols used will show a port is blocking, like for stp "show stpd <stpd> ports
A more low-level check of the port state can be done by checking the VPIF state. VPIF is a vlan port interface.
This can be done using the debug command "debug vlan show vpif <vlan> <port>
An example how to check this can be seen on this article, Is the EAPS Master node correctly blocking.
Even though the protocol that could block the port can be different, the vpif state can be checked the same.
This debug command will also show which protocols are used on that vpif.
A special case is a share with LACP, if the lacp partner does not negotiate the port will also block, in show vlan the b will be behind the port, but the vpif state will still show forwarding.
This is explained in Why does a port show as blocked when the VPIF output shows it's learning and forwarding