Modpack: Nomifactory 1.7-alpha-3
GTFO version: 1.11.1

Seeing the usage of the greenhouse in JEI only shows the multiblock preview, but not the recipe for sapling and wood

The greenhouse still works if you have right input and correct circuit configuration

Also, I don't know why the greenhouse produces leaves instead of sapling (is this intended?)

I will investigate; can you look at the recipes for other machines?

As for your second question, yes, GTFO recipes naturally give back far more leaves than saplings, and there is a recipe (on circuit 1, I think) that's best suited for creating saplings for use in other greenhouses (or just getting a minor amount of wood).

Other GT multiblock still show me the recipe normally. I also look at the kitchen multilblock usage recipe, but I don't really know if it actually has recipe to show

The kitchen does not have normal recipes, correct. It appears your issue is something specific to Nomifactory CEu, so I'm going to attempt to install it now. You could also send me your log file as well.

Alright, I've identified the issue as coming from Nomi Labs.

I remember IntegerLimit said something about a new grennhouse in nomi. When i search JEI, i thought they didn't include it in the alpha release. Maybe it is hidden in the JEI?

Well, they at least added the recipe category for the Nomi Labs greenhouse, and it happens to have the exact same ID as that of GTFO's. I'm currently working out this issue with him :)

Should be fixed in nomi labs release 0.6.22 (which will release in a little bit).