Can we see transfer progress with kubectl cp?

It's not possible, but you can find here how to implement rsync with kubernetes, rsync shows you the progress of the transfer file. rsync files to a kubernetes pod

I figured out a hacky way to do this. If you have bash access to the container you're copying to, you can do something like wc -c <file> on the remote, then compare that to the size locally. du -h <file> is another option, which gives human-readable output so it may be better

No, this doesn't appear to be possible.

kubectl cp appears to be implemented by doing the equivalent of

kubectl exec podname -c containername \
  tar cf - /whatever/path \
| tar xf -

This means two things:

1. tar(1) doesn't print any useful progress information. (You could in principle add a v flag to print out each file name as it goes by to stderr, but that won't tell you how many files in total there are or how large they are.) So kubectl cp as implemented doesn't have any way to get this out.

2. There's not a richer native Kubernetes API to copy files.

If moving files in and out of containers is a key use case for you, it will probably be easier to build, test, and run by adding a simple HTTP service. You can then rely on things like the HTTP Content-Length: header for progress metering.

One option is to use pv which will show time elapsed, data transferred and throughput (eg MB/s):

$ kubectl exec podname -c containername -- tar cf - /whatever/path | pv | tar xf -

14.1MB 0:00:10 [1.55MB/s] [       <=>                                   ]

If you know the expected transfer size ahead of time you can also pass this to pv and it will then calculate a % progress and also an ETA, eg for a 100m transfer:

$ kubectl exec podname -c containername -- tar cf - /whatever/path | pv -s 100m | tar xf -

13.4MB 0:00:09 [1.91MB/s] [==>                          ] 13% ETA 0:00:58

You obviously need to have pv installed (locally) for any of the above to work.