Each of the physical limit switches should be wired to separate GPIO pins on the UNO, and the other side of the switches wired to ground (if the switches are Normally Open). The corresponding GPIO pins will go HIGH when the switch is closed.
If you’re using Normally Closed switches then wire the other side of the switches to the +5v pin and the corresponding pin will be pulled LOW when the switch is activated.
With the code, you have two options. I’ll assume that you’re using Normally Open limit switches:
use a timer (or timers) to check the state of the GPIO pins if either of the pins go HIGH then cut the power to the motor. I assume you’ll be using a relay, connected to a different GPIO pin to control the motor, but you could be using a motor controller shield or a high power transistor/MOSFET to do this.
use software interrupts on the pins that the limit switches are attached to. With a Normally Open limit switch that would be a rising interrupt. When the interrupt is triggered by the switch then a software function would be executed.
As you’re using Blynk, I’d say that option (1) would make more sense. The frequency of the timer(s) that check the limit switches will depend on how fast the mechanical device is running and how critical it is that it stops immediately after the limit switch contact is made. Try having your timer(s) run every 100 microseconds. If you’re using two timers then stagger them so that they don’t both try to run at the same time (one set to 100 microseconds and the other at 120 microseconds for example).