Display hierarchical entity reference fields inside node I have the following content types in Drupal 8 :

User


field: image  
other fields  


Organization  


field: logo  
Entity reference to User [one to many]  
other fields  


Event


Field: Date  
Field: Description  
Entity reference to Organization [one to many]


The event nodes need to look like this (display the following):


Event Title  
Event Date  
Event Description  
All the organization logos (from the organizations added as a reference entity to the event)  
All the user logos that belong to the already referenced organizations  


Is there any way to do this with already existing Drupal 8 modules or do I have to write some custom code ?
You could render this with four different display modes:

1.) The Event view mode to start with:


Event Title
Event Date
Event Description
Reference field for Organization, configured to render the view mode logos1
Reference field for Organization, configured to render the view mode logos2


2.) The Organization view mode logos1 contains one field for the Organization logos:


Image field logos


3.) The Organization view mode logos2 contains one field for the User logos


Reference field for the content type User, configured to render the view mode userlogos


4.) The content type User view mode userlogos


Image field for user logos


To implement two instances of the reference field you need the module Display Suite. Or combine logo1 and logos2 in one view mode with two fields, but then the logos will get mixed. Or use for the second reference field a View, with the help of EVA.