How to display the list of attachments of Custom object in Salesforce?

To see all attachments on a record, ensure that the Notes & Attachments related list is added to each of your page layouts. To do this, click on Setup, open the Object Manager and select the Object you’ll be using. From the left panel, select Page Layouts.
Click on the Related Lists section and drag the Notes & Attachments Related List into the Page Layout if it is not already there.