I've used the following code to create a list of items to approve for a given object.  However, it's based on matching object related records which have active workitems rather than just based on the object itself.  Let me know if you find a better way to link it to the object rather than the object records?

//populate list of approval items private List<ProcessInstanceWorkitem> lstApprovalItems;

private List<Id> memberOfQueue = new List<Id>();

List<GroupMember> groupMembers = [Select Group.Id From GroupMember where UserOrGroupId = :UserInfo.getUserId() and (Group.Name in : config.get('ApprovalProcessQueues').split(',')) Limit 10];

//list queue ids current user is a member of
if(groupMembers.size() > 0){
for(GroupMember g : groupMembers){
memberOfQueue.add(g.Group.Id);
}
}  

lstApprovalItems = [select p.id, p.ProcessInstance.TargetObjectId, p.ProcessInstanceId, p.OriginalActorId From ProcessInstanceWorkitem p where IsDeleted = false and (p.OriginalActorId =: UserInfo.getUserId() or p.OriginalActorId in :memberOfQueue) and p.ProcessInstance.TargetObjectId in (select id from Ticket_Data_Form__c where recordtypeid =: config.get('DF_RecordTypeId') and Approval_Status__c != 'Approved' and Approval_Status__c != 'Rejected' Limit 1000)];

 You could alternatively use a subquery to match on the first three letters of the salesforce object record id values.

(select id from Ticket_Data_Form__c where id.substring(0, 3) = 'cON' and Approval_Status__c != 'Approved' and Approval_Status__c != 'Rejected' Limit 1000)

 * Note this works well if approval process is assigned to a user or queue.  However, if queue, the queue assignment needs to be associated to actual users (not roles, roles and subordinates, etc)  You would need to update the code to find if current user is member of queue based on role assignments. (if you update please let me know).