Is it possible to extract Planned Start Date and Planned End Datesof an Iteration somehow in jazz reporting service?

You can do this by creating a new report based on the work item traceability to the Iteration object and then edit the query in advanced mode to remove the dependency to the work item.

1) create a query, datasource DWH, select your project, select work item
2) add traceability from work item to Iteration
3) remove any condition
4) In format add attribute start/end date of iteration
5) In format remove all attribute from workitem
6) in advanced mode remove the iteration test in the on clause

Before:

SELECT DISTINCT T2.NAME,       T2.END_DATE,       T2.START_DATE,       T2.PARENT_ITERATION_NAMEFROM RIDW.VW_REQUEST T1INNER JOIN RIDW.VW_ITERATION T2ON (T2.ITERATION_ID = T1.ITERATION_ID) AND T2.PROJECT_ID = 433 WHERE T1.PROJECT_ID = 433  AND(T1.ISSOFTDELETED = 0 AND T2.ISSOFTDELETED = 0) AND(T1.REQUEST_ID <> -1 AND T1.REQUEST_ID IS NOT NULL) AND(T2.ITERATION_ID <> -1 AND T2.ITERATION_ID IS NOT NULL)

SELECT DISTINCT T2.NAME AS NAME1,       T2.END_DATE,       T2.START_DATE,       T2.PARENT_ITERATION_NAMEFROM RIDW.VW_REQUEST T1INNER JOIN RIDW.VW_ITERATION T2ON T2.PROJECT_ID = 433 WHERE T1.PROJECT_ID = 433  AND(T1.ISSOFTDELETED = 0 AND T2.ISSOFTDELETED = 0) AND(T1.REQUEST_ID <> -1 AND T1.REQUEST_ID IS NOT NULL) AND(T2.ITERATION_ID <> -1 AND T2.ITERATION_ID IS NOT NULL)

Timelines and iterations are not reportable objects as far as I can tell. If you can't see these as Artifacts to choose, you can not report on that data. Individual items can be in other artifacts e.g. values of iterations in timelines. You will be able to report some data for these individual objects. However, for very complex objects you might not find all data that is available in the tool itself.

Unfortunately your question is to imprecise to be able to answer more.

 You can do this indirectly using the Report Builder traceability.  If you trace a Work Item to its iteration, from there you can get the Start Date and End Date (and other attributes).  But I'm not aware of any way to do a standalone report only on Iteration details.