Are knobs basically universal?

Do most knobs fit everywhere? Do strat knobs fit on tele fit on jaguar fit on jazzmaster? fit on les paul? fit on pedals?

First difference that comes to mind is that some are metric and some are imperial so they don't all work on different diameter shafts.

Is it possible to tell before buying knobs if they'll fit?

Some push-fit to a 'knurled' shaft. Others have a grub screw that fits to a plain or flat-sided shaft. Some are taller than others. If you're going to a shop then take one with you for comparison?

I'm looking on ebay for some knob to replace my Fender Jaguar knobs.

Anyway you can tell if these fit?
http://www.ebay.com/itm/150795082209?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Look at these: http://www.ebay.com/itm/Genuine-Fender-Jaguar-Black-Skirted-Knobs-Set-Two-/330696817104?pt=Guitar_Accessories&hash=item4cff10f9d0

Look at these: http://www.ebay.com/itm/Genuine-Fender-Jaguar-Black-Skirted-Knobs-Set-Two-/330696817104?pt=Guitar_Accessories&hash=item4cff10f9d0

But those are the ones I have right now...

Point is I wanted cooler looking knobs. I want knobs that look like the Fender Amp knobs. I'm just not sure which ones fit.

These ones have a set screw and will fit on solid or split shafts. The price is for one knob. You could measure the diameter or your pot shafts then contact a few sellers asking if their knobs will fit your needs.
http://www.ebay.ca/itm/NEW-Genuine-Fender-Skirted-1-10-Amp-Knobs-SINGLE-KNOB-/140725652895?pt=LH_DefaultDomain_0&hash=item20c3e70d9f

But those are the ones I have right now...

...but if you read the auction description it tells you what size your knobs are and how they're attached. Use that information to search for your new knobs.

Do most knobs fit everywhere? Do strat knobs fit on tele fit on jaguar fit on jazzmaster? fit on les paul? fit on pedals?

No, they're not universal.
1. Metric or Idiotic, er, English?
2. Split shaft (Gibson style, press fit) or solid shaft (Fender style, uses set screw)?
3. Appropriate shaft size - there are many different sizes of pot shafts

Is it possible to tell before buying knobs if they'll fit?
Sure. You need to know the size of the pots you want knobs for. Diameter of the shaft is what you're looking for. A micrometer is probably the best tool to use to measure it.

These ones have a set screw and will fit on solid or split shafts. The price is for one knob. You could measure the diameter or your pot shafts then contact a few sellers asking if their knobs will fit your needs.
http://www.ebay.ca/itm/NEW-Genuine-Fender-Skirted-1-10-Amp-Knobs-SINGLE-KNOB-/140725652895?pt=LH_DefaultDomain_0&hash=item20c3e70d9f

www.angela.com carries those in their "Guitar Amp Parts" section. They will fit a 1/4" solid shaft and have a skirt diameter of 1 3/16". And retail @ $3.00 per knob. You could email Angela to confirm the fit for your application.

If you have split shafts you could get the brass bushings to avoid the making sure the set screw is in the slot routine. I'm not familiar what type of pots are on a Jaguar, so you'll have to do a little research. Good luck!

'72 Deluxe Tele knobs are similar to the ones you want.
Fender part numbers 0054521000 and 0054522000
One EBay at random
http://www.ebay.com/itm/Genuine-Fender-Tele-Custom-Deluxe-Volume-Knob-0054521000-/370548464603