I apologize for my stupidity. I just swapped out my casette from my training wheels to my race wheels for the first time, and in the transfer, the two “spacers” slipped out. Any help as to where in the cog set the spacers go on a dura-ace 10sp casette?
You’ll know as soon as you put the cassette back on the freehub body! 
If the spacers have “10spd” etched on the outside, then they go between the cogs that are not grouped together on a carrier or that do not the spacer built into them. If however, one of the spacers is very thin, it goes behind the cassette (between the hub body and the largest cog on the cassette) when installing it on an 8/9 speed freehub body. Hope that explains it for you.
I just did this as well. In my case, I put my 9 speed on an older wheel that was an 8 speed. My 9 speed cassette has a spacer at the very end (between the spokes and the gears), but that spacer didn’t fit on the older wheel. I left it off and everything seems tight and the shifting is fine. Was that ok?
Thanks,
Josh