Drinking and eating regime in an older dog.

Jack Russells can go on for a long time so I don't think you need to adjust his diet for his age. Just give what has worked for him in the past, but keep an eye on his weight - you might have to reduce his portions if he gains weight.

I assume by granules you mean kibble? It's not possible to say how much of each he should have as kibble is intended to be a complete meal, and many people who feed meat and vegetables don't feed kibble at all. But it sounds like he's getting a good variety of foods, which is great.

Offal should generally make up about 10% of the diet, but if you give too much you can normally tell from the sloppy poos - if the poos are nice and firm but not too hard, you're getting it right.

What is black fruit?

I'm not sure what you mean by him knocking his feet - at a guess, this could indicate a problem with a knee joint, maybe luxating patella. Have a look at this video showing luxating patella in a Jack Russell to see if it looks similar:

You say he drinks when he eats something salty - salt can be harmful for their kidneys so depending on what this is, you might want to reduce or remove it from his diet. Chances are that he's getting all the water he needs from the wet food but what you could do is to 'flavour' his normal drinking water with some meat juices till he chooses to drink it, then very gradually reduce the amount of meat until it's pretty much just water. This might get him back into the habit of drinking again without encouraging him to drink too much.

But either way, you'd really need to take him to a vet to be diagnosed and treated.

 

I wouldn't call being 10 in the terrier world as old. All of mine were like spring chickens at that age. The one I've still got with me now is 17 years old, still jogging when we go out. She had cancer for the past 2 years and eats what the hell she likes. So I wouldn't call 10 as being old for a terrier