I am stuck on grammar N5 and N4, cant get the confident feeling of understanding it , some parts i forget fast so i relearn them every 6 months, any tips on how to move on from beginner grammar.
Wanikani helped alot so i understand kanji and words meaning its just the grammar that gets me.
Any sites to quiz myself and to test my knowledge or something like that.
What resources are you currently using for grammar? That might help us with giving you advice.
Well, this might sound like a trivial advice, but I think the best way to have grammar stick – is to constantly see it in action by reading more native Japanese material.
You are well within WK level where people start reading simple Japanese material.
Things like
https://www3.nhk.or.jp/news/easy/
or
In any case, best of luck with your studies! 
Which grammar points exactly are struggling to stick?
Anyway, a general answer, for basic grammar, could be production. Write, make mistakes, get corrected. The resource for that would be LangCorrect.com. There are threads in WaniKani like sentence a day thread or Japanese Language > Japanese Only (Beginners), and perhaps forums of Renshuu.org, Bunpro.jp, MaruMori.io, etc. (Or maybe spoken, though I don’t know that part well.)
For intermediate grammar, it could be observing natives speaking. More advanced one, written, literature, news. But none can be really replace another well.
The best way to remember grammar, if it’s about using it, is to use it, read and talk. I still struggle to use a lot of different ones when speaking, but I realise that while studying N3 grammar, I understood the N4 grammar points that weren’t sticking, and the same applies with studying N2 grammar.
Don’t get too frustrated and discouraged, and just keep moving forward.