How to find no. of hash partitions per database partition, of a table, in partitioned database environment?

What do you mean by "hash partitions"?

hash partitions: Also called as hash keys that are generated by hash alogrithm, during the distribution of table rows, as per the distribution key across the database partitions.

Maybe you're looking for 32767 (4096 in pre-v9.7) - partitioning/distribution map mentioned here:
IBM DB2 9.7 for Linux, UNIX and Windows Information Center


"Database partitioning is the method by which the placement of each row in the table is determined. The method works as follows:
A hashing algorithm is applied to the value of the distribution key, and generates a number between zero (0) and 32 767.
The distribution map is created when a database partition group is created. Each of the numbers is sequentially repeated in a round-robin fashion to fill the distribution map.
The number is used as an index into the distribution map. The number at that location in the distribution map is the number of the database partition where the row is stored."