I have a quest to "kill the giant at secundas shelf" but no location appears on the map and the clairvoyance spell doesnt work either. Does anyone know where this is located?

http://www.uesp.net/maps/srmap/srmap.shtml?centeron=Secunda%27s+Kiss

There currently is a glitch about giants not respawning at camps you've already cleared, which as far as I know has no work around unless you're on PC and console command it to advance the quest.

I think it is between Bleak Falls Barrow and Whiterun, the Giant Camp is on the Whiterun side of the mountains.

I thought it might be a bug. Do you know the PC console command to use?

Indeed I do. There's two different ones, depending if the steward or Jarl gave you the quest. I'll list both for you.

Command for "Collect Bounty from X Steward" -- setstage BQ03 100
Command for "Collect Bounty from X Jarl" -- setstage BQ03 101

Thanks for the help.

You're totes welcome! <3