I'm just a Silver jungler, so I don't know how much I can help. I'll try.
All I can really say is that wards do a lot when you want to track the enemy jungler. Another thing to have in mind is how to lanes are working. Some lanes are easier to gank or more appealing to do so, so you can judge where the jungler might be based on those assumptions:
- Top lane is a Malphite vs Garen
- Mid lane is Lux vs Le Blanc
- You are a Lee Sin vs Kha'Zix
- Bot lane is a Miss Fortune & Taric vs Ezreal & Janna
In this situtation you know that top is not a prime target for Kha'Zix to gank, since Malphite will be building tanky and both laners are tanks, so the only proper damage would be from Kha. Kha'zix is a snowball assasin and Lux is a very passive laner, so Kha won't have many chances of getting a kill, unless Le Blanc sets that up. Bot lane is the easier to gank.
For you, the top lane is equally hard and pointless to gank. Le Blanc is hard to catch unless she uses her W to harras. Bot lane is also hard to gank since they have Janna and Ezreal.
With all this in mind, the best chances for Kha'Zix to gank would be Bot lane and for you would be Mid. You can spot Kha'Zix if he tries to gank bot by having that side warded and then you keep an eye on Le Blanc. If LB is overly passive, that's because she's setting up for a gank. The same way, if bot lane sudenly starts playing very agro, that's because Kha'Zix is coming there.
Countering the other Jungler is probably the most valuable thing you can do, since you have the element of surprise. To do that, you need cooperation from your team by having multiple wards and you need to constanly analyse how the lanes are developing.
That said, in lower ratings junglers are not that skilled and they just go with the flow, so they are more imperdictable.
Jungling takes a lot of guessing, but you can "up your chances" by being exeperienced in the role. Knowing jungle paths and how each jungler behaves in the jungle is important. You can also understand which lane the other jungler is favoring by the ammount of ganks he performs.