How to use db2look to get the ddl of sequence?
You want to use the -e option. That will export sequences along with a few other things. Depending on your sequences you could either use the -z option for schema or the -a option for all schemas. You may also want to use the -o option to output to a file.

We tend to use the following a lot where I work

db2look -d my_db_name -e -o my_db_name_look.sql



  EDIT: Based on the comments you have below, you can use db2look, or you could also use the system catalogs to retrieve what you need.
  
  Why not run the following:

select seqschema,seqname from syscat.sequences where cycle = 'N'

  
  That will retrieve those same sequences for you, but through querying
  and you won't have to use the db2look utility to retrieve everything
  you want. Of course if you want the DDL, you'd still have to use
  db2look to do that, but at least you can then use -z better to narrow
  down you schemas or do a search to find the names that came from your
  query.