To detect the progress or how far dd has come in a running copy, open a second terminal window, run top to get the id of the dd process, then issue the command kill -USR1 xxxx (replace xxx with the actual ID of the process), now it may appear that nothing happened, but swicth the terminal to the one dd is running in
you should see something like
1036902161+0 records in 1036902160+0 records out 530893905920 bytes (531 GB) copied, 29702.1 s, 17.9 MB/s