Vocabulary

Hi, today I want to write some small sentences to learn some vocabulary. So let's try!
I already forgot my knees. (I'm not sure what you are trying to say here?)
The law area is the better way for working Practing law is a great carrer choice.
Fortunately, I have another knee. (Although this sentence is grammatically correct, I'm not sure what you mean.)
Until the age of 16, I never tried to learn another language like English.
We are together and that's the most important thing in the world.

Keep practicing! You're on the right track. 

vocabulary

Hi
Today, I want to right write some smallest very short sentences for in order to learn vocabulary. 
So let's try !
I already have forgotten my knees. <---- I do not know what this could possibly mean 
The law area is the better way for working Law is the best area in which to work. 
Fortunately, I have another knee. 
Until the age of 16, I never tried to learn another language like English.
We are together, and that's the most important thing of in the world.

vocabulary

Hi
Today i want to right write some smallest sentences for to learn vocabulary
So let's try !
I already forgotten my knees 
The law area is the better way for working (Not sure of what you mean by law area? The profession?)
Fortunately, I have another knee
Until the age of 16 I had never tried to learnt another language like English
We are together and that's the most important thing of in the world

I think you might have the wrong word for "knee" here. Do you mean the part of your leg? It seems unlikely that you would forget your knees. :)