Perform the query below :

db2 "SELECT COLNAME, PARTKEYSEQ FROM SYSCAT.COLUMNS WHERE TABNAME = '<TableName>'  AND PARTKEYSEQ != 0 \
ORDER BY PARTKEYSEQ"

Example:  If you wanted to obtain information about the partitioning key that has been defined for a table named EMPLOYEES, you could do so by executing the following query: 

db2 "SELECT COLNAME, PARTKEYSEQ FROM SYSCAT.COLUMNS WHERE TABNAME = 'EMPLOYEES'  AND PARTKEYSEQ != 0 \
ORDER BY PARTKEYSEQ"

Assuming the table EMPLOYEES was created by executing the following CREATE TABLE SQL statement:

CREATE TABLE employees (

    empid      INTEGER NOT NULL

    name       VARCHAR(75),

    ssn        CHAR(12),

    dept       CHAR(3),

    salary     DECIMAL(8,2),

    hire_date  DATE)

  PARTITIONING KEY (empid, ssn)

the results produced by the query should look something like this: 

COLNAME                    PARTKEYSEQ

-------------------------- ----------

EMPID                      1

SSN                        2

  2 record(s) selected.

This indicates that the partitioning key for the EMPLOYEES table is comprised of the columns EMPID and SSN.