Running/jogging ..

Running on the elliptical is good and I guess the treadmill is fine if the incline isn't to steep. Aqua jogging is good too.

I run with fairly bum knees, but my doctor doesn't seem to think that's an issue. I have a very heavy step and sometimes that seems to affect how much my knees hurt, but I just run through it. Sometimes I wear a brace on the worst knee, but usually run without it. Just be careful.

(For what it's worth, my daughter has some serious knee issues and her physical therapist says the elliptical is okay, but she's to avoid the treadmill at all costs.)

I hear the "bad knees" thing quite a bit.
I've had knee issues off and on since I began running a year ago. My experience and advice can be summed up as follows....
(1) If it hurts, stop doing that, and get appropriate rest before trying again
(2) nearly anything in your body can be made stronger with training/fuel/time
(3) At the gym, the treadmill looks the most like running, but its probably worse, unless its very springy to absorb, in which case, it may weaken your ankles.
(4) When recovering and you still want to "run", the best machine is the elliptical. Like a standing bike, it eliminates impact, but will feel weird until you get used to it.
(5) For strengthening, there are all kinds of leg exercises. What shows up as a symptom of pain in the knee may be ultimately caused by a weakness elsewhere (hips). Methodically work it all as much as you can.
(6) For cardio and some strength with no impact, swimming is best.
(7) if you are just getting into running, do no more then 3-4 days a week for 6 months before beginning to add more days of running
(8) from a fuel perspective, its very important that your body gets fat and protein. and water. lots and lots of water

I've had reconstruction on both knees and ankles, and currently run about 40km per week.

Form is very important, as are appropriate shoes. I prefer trail running, but I'd also support the point above about resistance training being a great help in the stability realm.

I have a good pair of Nike.
We have trails,I was planning to try the nearby one.

But were those Nikes fitted by a local running store?

I have a good pair of Nike.

Brand isn't as important as structure, personally I've not found a pair of Nike that I could run in.

There are four main types of shoe, broadly; motion control neutral, cushioned, minimalist.

Motion control are appropriate for runners who overpronate, that is the foot rolls inwards on landing. The shoe helps mitigate that, and tends to have less cushioning. This is the majority of runners.

Neutral shoes are much as described, they let the foot operate naturally.

Cushioned are generally for underpronators, the foot doesn't roll as much as it should do. This starts to propagate problems up the skeleton, hence cushioning reduces the shock loading.

Minimalist shoes have little to no controlling or cushioning structure, so tend to force a forefoot landing.

In principle getting the correct shoe either involves getting fitted at a decent running shop, or lots of trial, error and pain.

Within that set some runners find some brands just don't work for them. Personally I've had success with Saucony.

Trail shoes don't tend to have that same range, they frequently have a lower drop from heel to toe. The main reason is that the surface in trails tends to be pretty dynamic, ad in many ways that's good for leg injuries as it encourages the development of the fine controlling muscles around the joints.

I have a good pair of Nike.

Brand isn't as important as structure, personally I've not found a pair of Nike that I could run in.

There are four main types of shoe, broadly; motion control neutral, cushioned, minimalist.

Motion control are appropriate for runners who overpronate, that is the foot rolls inwards on landing. The shoe helps mitigate that, and tends to have less cushioning. This is the majority of runners.

Neutral shoes are much as described, they let the foot operate naturally.

Cushioned are generally for underpronators, the foot doesn't roll as much as it should do. This starts to propagate problems up the skeleton, hence cushioning reduces the shock loading.

Minimalist shoes have little to no controlling or cushioning structure, so tend to force a forefoot landing.

In principle getting the correct shoe either involves getting fitted at a decent running shop, or lots of trial, error and pain.

Within that set some runners find some brands just don't work for them. Personally I've had success with Saucony.

Trail shoes don't tend to have that same range, they frequently have a lower drop from heel to toe. The main reason is that the surface in trails tends to be pretty dynamic, ad in many ways that's good for leg injuries as it encourages the development of the fine controlling muscles around the joints.

Listen to ALL of this!!! Wise words here!

Just bought a pair of Brooks Ravenna 5's, great shoe. I also run 5k 6 times a week with a knee and ankle that has suffered from multiple gout attacks. My knee is always swollen but no real pain. Xrays on 2 different occasions showed no damage so I just ice my knee or take anti inflammatories.