REORG command does not work in IBM Data studio but same works in Command Line Processor
I guess you tried to run it in an editor window.
YOu have to switch to


  DB2 server Command Line Processor


in the Configuration tab of the editor.
Do not forget to explicitly connect to your database 

connect to sample ;
reorg table suppliers;


Alternatively you could switch to "Administer Databases" and run the reorg from the contect menu of a table: