How to find the coordinates for a point in a R map or figure

Question

I am creating a map using the "tmap" package in R. I want to add a scalebar at a specific spot on the map using tm_scale_bar(position = c("x", "y"),. How do I find the coordinates for the point? So far I have been using trial and error which works fine for one figure but will become tiresome when making many figures. I seem to recall a function that interactively returned coordinates based on the position of the cursor over a figure. Any advice would be great!