NAIL!!!
No chisels, no screwdrivers....... maybe, perhaps, possibly use a skinny center punch to push out the staked material. DO NOT deform the grooves and threads.....you'll hate life....or you'll need a LH thread reforming tool!
I forget which side is LH..... look closely at any exposed threads and read them.
Also NUT may have stake marks on all 6 points indicating it is LH.....
See Lee's pic that he posted a few posts back for the difference!!!
Steve