Node registration form block - hide if registered I'm using "Node registration: this page's form" block, but I want to hide it when user has registered for this node already. I know i should use 'If' statement but i don't know what condition to use.
Node registration not providing a function in it's API for that, however you could include the "node_registration\includes\node_registration.api.inc" file and use their internal function that the module use to check for user access for  a specific node.

// Include the file
    module_load_include('inc', 'node_registration', 'includes/node_registration.api');


 if (_node_registration_user_registered($node, $account)) {
    //do something
  }