my uno runs the sketches but when i connect my nano , i cannot upload to it,

I cannot upload to my nano.i run blinky on the uno no problem, but the nano has no com port assigned? how do I get a port for the nano please ?

What USB to serial chip is on the Nano? Maybe it needs a driver?

As you're referring to com port, I assume that you're using Windows. In which case check device manager and see what it says when you connect the Arduino. If nothing happens, you might be using a charge-only cable. If you get (new) yellow triangles, I agree with groundfungus that this is probably a missing driver.

Note:
Be accurate with details when posting questions. In this case
1)
which version OS
2)
which version IDE
3)
original Nano or cheap clone