Another pass at YouTube shows better posted sources than the ones I previously found.
.
For the 1989 original version, postings are difficult due to the obsolete consumer formats and the analog-to-digital conversion required. This one boasts "AC3 Audio". It may be from laserdisc, but the picture appears to waiver, like videotape but without the telltale tearing at picture bottom. Anyway, it's the best I've seen online so far ..
YouTube:
Pixar Knick Knack Original 1989 AC3 Audio GOOD QUALITY
.
For the 2003 revised version, the next posting is an easy one because of it's digital media release, which makes for easy extraction at full quality (HD in this case) ..
YouTube:
PIXAR'S KNICK KNACK - 1080p
.
And there are commentaries! One is of John Lasseter and Eben Ostby talking about their original release in 3D (but I haven't seen that one online yet). That one would be very nice ... to see . [EDIT: found it]
YouTube:
Pixar Short Films Collection Vol. 1- Audio Commentaries [AUDIO]
[Knick Knack @ 12m50s to 16m19s]
.
The other commentary is Lasseter and Ostby talking about the short's inspiration from snow domes ..
YouTube:
Finding Nemo - Knick Knack wCommentary
.
These are great sources to get organized and even set up a repeatable run. Thereafter, the original, best captures could be plugged in for the best restoration.