Hi @zeineldn,
QIIME 2 does not yet have its own citation. Please cite the main website (https://qiime2.org) and for now please cite the original QIIME 1 publication until QIIME 2 has its own publication.
Please also note that almost all QIIME 2 plugins implement methods that were developed independently of the QIIME 2 framework. You can retrieve citation information for each plugin by using the command qiime info --citations, and note that it may be appropriate to add additional citations not listed there (for example, the q2-diversity plugin lists citations for UniFrac, but if you use other beta or alpha diversity methods in a publication, you should cite the original source of that method.
I hope that helps!