It would be very nice to be able to have two windows or panes open on the same file at the same time. This is useful when working on longer files where one doesn't want to lose her place when jumping around.
I'm searching around, but it seems it's not possible in rstudio. I've opened a feature request here for those who would like the same thing: https://github.com/rstudio/rstudio/issues/7842. This feature has been requested elsewhere, but I haven't found anything recent.
Just to close the loop on this; my colleagues responded in the github issue that we do have an upcoming 1.4 feature to show multiple source columns, so you can see multiple files at the same time. However, this doesn't support opening the same file in multiple columns. We'll keep the feature request open and consider it post-1.4. Thanks for the suggestion!