It may be begging the question, but why are you zooming in Layout. Are you opening into a window? If so, you shouldn’t. Best practice is to set up the scene you want in SU, export it to LO choosing the appropriate scale, and leave it at that.
As far as I know, this doesn’t exist in Layout.
You would have to somehow link an autotext to a specific sketchup view to do that and there is no apparent way to do that.
After I saw your post I tried the label tool in hopes that it might give as a selection the scale of the model but no. just definition name and area.
Well ok but it’s not a good idea. As soon as you open a window, you break the link between the SU file and the LO one. That means that if you update the SU file, it will no longer be reflected in the LO one.