The $process.executableDir expression correctly calls the value of the executableDir variable from the tabular process variable. The process variable is a tabular variable that contains the output of the ps command, which lists the processes running on a CI. The executableDir variable is a column name that holds the directory path of the executable file for each process. To access the value of a column name from a tabular variable, you need to use the dot notation, such as $variable.columnName12.
References1: Pattern variables - Product Documentation: Tokyo - Now Support Portal2: Examples of EVAL scripts used in Discovery patterns - ServiceNow