I am using RG191 Gateway and RS191 Sensor. I would like to know how to get and display the sensor data after registering both the Gateway and the Device on TTN. I would like to do this without using any additional hardware.
Thanks in advance for your support.
Possibly one of the easiest ways is to follow through with something like a Cayenne integration (TTNer’s have used several different dashboard/integrations so suggest search the threads 
). Set up you application, choose the Cayenne integration, head over to cayenne/mydevices in your account set up the integration & data pull from that side, choose the Laird/RS1xx as device from options list along with TTN as the source network and you will be rewarded with a good little dashboard of your data. You can even elect to ‘share’ the project , getting a link that you can email to others allowing read only viewing of the data…have used several times for quick and dirty monitoring by clients, friends & relatives.
e.g.:
You have another option to choose an RM1xx end device where you dont get the map from device location you set up in settings, but with same core info…useful if you want aa less clutter dashboard or dont want to disclose specific location for device
When configuring the RS1xx be sure to select the Cayenne LPP format for payload vs Laird own - as it requires confirmed download and a timestamp to start message flow so Cayenne LPP option quicker easier and less demanding on spectrum & to avoid breaching TTN FUP select a longer update sampling rate as current Laird implementation still requests ack every 10 samples (keep alive and check network connection otherwise force device reset & rejoin) - again risking FUP, Duty-cycle breach and generally being anti-social if using frequent updates! 
Thank you.