I struggle alot against people with pretty good j.CDs. Sometimes, it's better not to fight them in the air. Sometimes, it's better to just use your ground options.
First option should be to block. If it's the first time someone does a j.CD at you to get in range of you, you're pretty safe in blocking. Whatever they try, if you can't respond to it, blocking's the safest option. If they want to keep trying to j.CD you, you can poke them with st.A to get out of it.
Next thing is to DP. This is the easiest and riskiest thing you can do. I'd rather do it against someone jumping really high as you'll likely use C crow bites. If you use A Crow bites, you'll want to do it as they come closer to you to insure the invincibility doesn't wear out. C can be done at the top of their jump arc. Hell or high water, you'll hit them. You have to react quickly on this front though or you'll miss the opportunity. Also keep in mind their jump arc as K' might go right by them as they jump.
What I've been doing lately is backing up and doing qcf+C. C Ein Trigger is active for a really long time so when I use it after doing a backdash, they often land in it or collide with it. If they're doing it super meaty, they'll run right into Ein trigger before they hit you. This is a bit harder to get used to, but it's less risky than doing a DP, but probably not as damaging.
The last options are a bit harder because it involves either reacting quickly or reading. K' low B lowers his hitbox a lot. You can go under a lot of j.CDs like Daimon, Shen, Takuma, Mr. Karate if they do the j.CD early as an air-to-air. You can bait them to do this by hopping straight up once or twice from a reasonable distance and whiffing a j.CD. If they take the bait, they might try to respond by doing a hop CD. This abuses the fact that they can't block on the way down and they're already expired. You can link the d.Bs into a small combo or just whiff so you can do something a bit more advanced (Throw, st.C, HD bypass)
As for frame traps, the only three I can think of are ones using his light normals.
d.B, d.A => You're +1 after the d.A, but you're at far normal range.
d.B, (delay), d.B => Natural combo so it's a natural frame trap
d.B, st.C => Unnatural, but the blockstun into st.C makes late pressing difficult.
d.B, d.B, d.B, qcf+A => Max range of A Ein Trigger puts you at positive frames
Any normal, qcf+AC => +11 on block. You can literally guard break someone doing this over and over again.
(Opponent's wake up), qcf+C, d.B => This actually links on a knocked down opponent, do it just as they get up and they won't be able to do anything. Watch out for DPs.
st.B, st.D => In midscreen, does nothing useful. In the corner, low move blockstring other than d.B
d.B, st.A (whiff) => This needs its own explanation.
This frame trap is a bit risky because you're inherently safe, but you're whiffing a normal. If someone responds right after the blockstun, you're pretty toast. d.A has pretty poor range and might not encourage blocking low, but for more frame advantage so use this if you feel less safe.
Whiffing a standing jab, for a lot of people, usually solicits a response. You can check to see what people do during this period of limbo where you might not be hitting them. If they continue to block, you can do a number of things. You can hop up, do st.C, do d.B, walk forward and throw them, walk forward and do nothing, walk forward and do d.B, etc. The things you can do from a whiffed light are pretty endless. You can also be very bold and free cancel it into command normals like f+A or specials like a crow bite. Your st.A will hit them if they try to jump or switch to stand blocking. Aside from flash kicks and very fast buffering dps, it'll likely catch someone trying to do a reversal move as they stand. Again, if they're mashing right out the gate, they're probably going to tag you when you respond, but if you know this, you can have a counter ready for them.
That's about all aside from st.C, f+A, Ein Trigger. If they aren't blocking low, and this is super risky, you can sneak in a fast narrow spike because it's a natural combo. I've tried to delay it, but it might not come out. Aside from less effective stuff, just stick to 1,2 hit delayed normals to trick them.