I have never done this before. my question is. What weight rod do I need. Or could I use my standard spinning / jigging rig for shooting docks.

As long as you stay far enough away from the dock, to not hit it with the rod, I think you can use just about anything.

That being said, I like a 4.5'-6' rod for dock shooting.

You are going to get any number of answers to this question because it all boils down to a personal preference.You will have to experiment an draw your own conclusion as far as rod length but which ever way you decide just make sure you use a highly visible line to detect the slight crappie bite with this technique.Line visibility is what you want here because more often than not you wont get a thump all you`ll get to let you know you got bit is a line twitch.If you can`t see it you`ll mist it.Me personally ,I prefer a rod about 5.4 to 6 ft also

Awesome Help. I now have a starting point. On line color. You are saying Hi-visible green? I can make that happen. I will do some dry land practicing. Like shooting. I will put a target up and see if i can get good at hitting it.

A few dock shooting tips:
1) "Light" not "UltraLight" action. UL is too whispy. 4'5" - 6' length. I wouldn't recommend anything longer when you're just learning.
2) Spinning reel or underspin. I actually prefer a little larger reel. Really small ones wind the line up in a tight loop and those loops are detrimental to a good hook set when you're letting the bait free fall. A bigger reel tends to release line that's less twisted.
3) 4-8lb hi vis line. Lighter the better. As the bait falls, you will see your line "twitch" when you get a bite. You don't want to close the bail and tighten the line too early because it will pull the bait back toward you. You want that jig to fall straight down as far back under there as possible. Then you can work it back toward you, and you'll still be watching your line. When done right, you'll see the bite before you feel the bite more often than not.
4) 1/16 - 1/32oz jig head with a bulbous shaped plastic body. The more rounded shaped body allows the bait to "skip" across the water and get further back. Most of the plastic jig makers have a model that fits this. Don't bother with painted heads until you get good at shooting. That paint will likely get knocked off the first 50 tries, because 47 of those will hit the dock.
5) Hold the head of the jig with the hook away from you. Seems like a trivial point, but you don't want to find out why.
6) Keep the backbone of the rod (butt to first eye) parallel to the water. Let out about half the length of the rod in line. Pull the jig back so that the line from the tip to the jig is also parallel to the water. This helps to keep the trajectory of your jig flat and parallel with the water. Practice in the driveway shooting under a chair before you go.
7) Look for docks with at least 6-7'+ depth at the outside edge of the dock. The deeper the better. Shallow ones will hold a few, but usually smaller fish. Bigger docks and ones with lots of poles are best. It's all about shade.
8) Shoot into the darkest (hardest to get to) part of the dock. That's usually where they'll be.
9) If you get bit, keep working on getting in that SAME spot.
This is by far my favorite way to catch crappie! It's a challenge, but when you get into them it can be a blast!
Good Luck!

EW

1/16 jighead, 6 lb hi vis line, I've had most luck with small plastics that have some chartreuse in them.

I use the 5 foot to 5' 6", indestructible, light, ugly stick rods. Watch the line.