How can I search Windchill for ECNs with specific conditions as a regular user, not an administrator

I interpret this to mean you are looking for ECNs that have only one remaining approver and you want to create an actionable list to "push" the last approver to complete their task.  If you're looking for specifically for task assignees where the actual primary business object is the ECN (not change activity) then you could do an advanced search on the work item and set the criteria "Status != Completed".   This will return all work items (tasks) that are still outstanding.  In the results table you will see the "Subject" column which contains the information of the subject of the task, i.e. the primary business object.  You can export that and parse/pivot in Excel to find out which ones have only one approver left.  

Note: This will return all open work items across all business objects, so the results could be huge depending on the size of your environment and how many running workflows you currently have.

Tip: If you know the name of the possible workflow activities related to the process in question, in your case your ECN workflow, then you can also put in a group of OR criteria in which you input the task names (Name field) so that your results are more specific to the business object you are interested in.

Perhaps these articles can give you the cue to get what you are asking for.

Query Builder report of all the assignees of Change Notice/Change Activity

Query builder" report to fetch all the Open Task

https://community.ptc.com/t5/Windchill/Change-Notice-Report-qml/td-p/451172

https://community.ptc.com/t5/Windchill/In-the-query-builder-report-how-to-get-an-assigne-name-in-a-role/m-p/263254

Hi @Naim23, 

I wanted to follow up with you on your post to see if your question has been answered. 
If so, please mark the appropriate reply as the Accepted Solution. 
Of course, if you have more to share on your issue, please let the Community know so that we can continue to help you. 

Thanks,
Anurag

If you want to write a query builder report, you can have it return any condition you want. It sounds complicated since you are looking deep into other objects like assignees and possibly change tasks. Ok, I think you are saying that now that you have this query builder report, you want non-admins to run it, like it was created at site or org level. There are two options. You can bypass access control which is a setting on the Query Builder report. Or you can defined an unrestricted group:

https://support.ptc.com/help/wnc/r12.0.2.0/en/#page/Windchill_Help_Center%2FQBProperties.html

I think a 3rd option is to make the report used in advanced searches which the user can execute when looking for ECNS.