In NTRU digital envelope, do everyone know the hash function $H$ used?
Yes, these are public parameters of the system.

Note that NTRU is not implemented exactly this way any more. The most up-to-date current spec is EESS#1, which can be obtained from https://github.com/NTRUOpenSourceProject/ntru-crypto/blob/master/doc/EESS1-v3.1.pdf.