It's quite straightforward.
Find the folder where the item you want is via calling https://forge.autodesk.com/en/docs/data/v2/reference/http/projects-project_id-items-item_id-parent-GET/. Here is the code snippet of using Forge nodejs client SDK:
const { FoldersApi, ItemsApi } = require('forge-apis');
const items = new ItemsApi();
const itemParentFolderContents = await items.getItemParentFolder(projectId, itemId, {}, oauthClient, credentials);
const itemParentFolderData = itemParentFolderContents.body.data;
Then you can call the parent folder endpoint you mentioned to get the folder parent of the folder where the item is located at.
https://forge.autodesk.com/en/docs/data/v2/reference/http/projects-project_id-folders-folder_id-parent-GET/ Here is the code snippet of using Forge nodejs client SDK:
const folders = new FoldersApi();
const parentFolderContents = await folders.getFolderParent(projectId, itemParentFolderData.id, {}, oauthClient, credentials);
const parentFolderData = parentFolderContents.body.data;