Hi mates, I would use a node that works good, but unfortunately the author decided to output an object which I can't easly address in NR, this is the picture:
This should work let ADC0 = msg.payload["/dev/i2c-1"].ads1115["0x4A"].singleEnded.channel_0.miliVolts;
Though I note that it is 0x48 in the debug.
The node red docs page Working with Messages shows you how you can easily copy the path to a property from the debug pane, so avoiding this sort of problem.
It is a matter of scoping. In this case it won't make any difference, but nowadays there is no reason to ever use var as far as I am aware. One should use the more modern let or const. If you only set the value of the variable once then it should be const.
var was introduced, I believe, when javascript was a very simple language and nobody bothered about scoping. Nowadays it is better to scope a variable to the area it is used in order to prevent accidental overwriting by another piece of code.