You can use REST API for this.
1) Get All Projects information from Project Online
http://<pwa_site>/_api/ProjectData/Projects
2) Get Project GUID
http:///_api/ProjectData/Projects/?$select=ProjectId
3) Get Specific Project information based on GUID
http://<pwa_site>/_api/ProjectData/Projects(guid'<GUID here>')
4) Get Assignment Information of a Project (Tasks Assigned)
http://<pwa_site>/_api/ProjectData/Projects(guid'<GUID here>')/Assignments
5) Get Assignments based on user
http://<pwa_site>/_api/ProjectData/Projects(guid'<GUID here>')/Assignments?$filter=ResourceName eq '<Name>'
6) Get Tasks of a Project
http://<pwa_site>/_api/ProjectData/Projects(guid'<GUID here>')/Tasks
Reference Link: https://www.dsouzajoel.com/2016/10/21/project-online-api-list/