How can i check usage of the PsiField by the JetBrains api ?

https://www.jetbrains.org/intellij/sdk/docs/basics/architectural_overview/psi_references.html#searching-for-references

WDYM with "modifying of this field"?

I mean assign a different value to this field. 

How can I check this assigning to my field ? 

Have you some turnkey solution ? 

You can check usages for being a com.intellij.psi.PsiAssignmentExpression

Thanks , and do you have some turnkey solution to check that somebody use synchronized block on object of my class or locks the lock on it ? 

Not sure I understand what you're looking for exactly, but you can find a number of related inspections around synchronization/threading in com.siyeh.ig.threading package in InspectionGadgets plugin from IJ Community sources