Ok, the output is different from Solaris, which is where I normally work; but that's not entirely unexpected, I guess.
The pool named "freenas-boot" in that output is listed as being on "ada0p2", which means it's on the device /dev/ada0, on the 2nd partition (the p2 bit). A historic Sun/Solaris naming convention s that "slice 2" (normally "s2") on the end of a disk name is an alias for "the entire disk". I don't know if FreeBSD/FreeNAS's implementation of ZFS is using a similar naming convention or not, but if you're looking for a ZPOOL from /dev/ada0, that's it.
Interesting that the pool name is also "freenas-boot"; I can only assume that the dead FreeNAS instance was using that as the pool name too for some reason. Again, not an expert in FreeNAS.
However, from a ZFS/ZPOOL perspective, that pool may well be importable still, as long as the pool name becomes unique. The way to ensure that (historically, from a Solaris perspective) would be to do this:
zpool import -N 7066402595766737261 <newname>
where "7066402595766737261" is the numeric ID for the 'freenas-boot' pool that's on ada0p2; and "<newname>" is your choice of new pool name. The '-N' tells it not to mount any ZFS filesystems in the zpool, because there may be name-space collisions; but if the pool imports, then you can amend the mountpoints and mount the filesystems independently if required.
That should, in theory, import the pool and give it a new name at the same time; but quite how you'd then attach the newly imported pool & associated filesystems into the FreeNAS config is beyond my experience, not having used FreeNAS much.
(I tried setting up a FreeNAS VM on my MacBook using Parallels, but it wouldn't boot from the ISO I'd downloaded, so can't really replicate/test your environment, I'm sorry)
Sorry I can't help much further than that on the FreeNAS side of things....