The enable pin isn't connected to the Arduino and isn't needed for serial communication. According to the datasheet, the enable pin is only used to disable the module by pulling enable low and by default enable is disconnected enabling the module.
This section from the data sheet explains how EN works.
The ENABLE line (referred to as the SHUTDOWN line in the M6e) must be pulled HIGH or left unconnected for the module to be operational. To shut down the module, the line is set LOW or pulled to Ground. Switching from high to low to high is equivalent to performing a power cycle of the module. All internal components of the module are powered down when ENABLE is set LOW.The Enable line must be connected to a GPO line of the control processor. This will allow the processor to reset the module into a default state should it become unable to communicate with the processor for any reason. Pulling the Enable line low for 50 milliseconds will reset the module.You might also want to have a look at the schematic and the Eagle files as those will help you determine what pins are present and where they are on the board.