Info on revoshift knobs?

I'm not quite sure what you're asking.

Revoshift is a Shimano word for their grip shifters, as opposed to STI levers for drop bars, or thumb/trigger/pod shifters for flat bars.

^{Example 3x7 set of Shimano TOURNEY SL-RS45 from Bike-discount.de, retail price was about 13 GBP in May 2021.}

Each shifter has one port where the cable exits. This also acts as a socket for the outer housing, and has a barrel adjuster for fine length changes while riding.

Also, there is some way to get the inner cable's barrel end into the shifter so it can't be pulled out. On a revoshift there's normally a way to separate the two parts, the darker rubber hand grip used to change gear, from the pictured lighter grey plastic housing. Colour varies with model, age, and wear.

You can see the inner cable's barrel end is nestled in the red plastic internal holder. This is one of the main places of failure, and this plastic can't reliably be glued back together. If only it had been made with metal, or thicker/better plastic.

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Could be there's confusion over why you have two shifters. On most bikes, the rear derailleur is controlled by the rider's right hand. And the front derailleur is controlled by the left hand, where fitted.

It is incredibly rare to have this handedness flipped over, I've only ever seen it once, on a friction-shifter. Indexed shifters are built to provide a number of detents (total clicks) and you can't use a 3x position left shifter to control a 7+ position rear derailleur.

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Opinion: Revoshift units are particularly plasticky and cheap, built down to a price. They generally work okay when new, but often fail within 12 months. This has tainted the perception for twist/grip shifters as budget, and I certainly held that opinion until I tried a Shimano Nexus 3 speed shifter, and some SRAM 3x9 grip shifters.

So it is not grip shifters that are bad, it is Shimano Revoshift shifters. You'd do better to use anything else where possible, or if you've already got them on your bike, be gentle to extend their life. But expect to replace them eventually.

In the absence of a photo to illustrate exactly what you mean, your question makes me think of Shimano Ci Deck where an additional little cable comes out of the shifter and pulls a little display to show what gear you are in. Styled a bit like a gauge cluster from a vehicle.

Recent service manual from 2017

At the beginning, some barrel-shifters were desmodromic*, meaning they had two cables each. One to pull the derailleur in either way and not relying just on a spring in the mechanism to do the job and to ease the shifting. The advantage resides in the fact that the spring especially in the RD wasn't always strong enough to overcome the friction of the cable in the housing that went full-length from shifter to derailleur. Coated or stainless cables were more of a dream, rusty ones frequent. Forcible shifting being a bonus on a muddy trail.

*Desmodromic valve-trains were common in high-powered piston aero-engines and are still used in very high-end and high RPM engines in race-cars and especially (Italian) motorcycles.