- Space selector logo: https://github.com/elastic/kibana/blob/7.8/x-pack/plugins/spaces/public/space_selector/space_selector.tsx#L100
- Login logo: https://github.com/elastic/kibana/blob/7.8/x-pack/plugins/security/public/authentication/login/login_page.tsx#L90
- Authentication status page: https://github.com/elastic/kibana/blob/7.8/x-pack/plugins/security/public/authentication/components/authentication_state_page/authentication_state_page.tsx#L23
- Welcome screen: https://github.com/elastic/kibana/blob/7.8/src/plugins/home/public/application/components/welcome.tsx#L139
- Top left: https://github.com/elastic/kibana/blob/7.8/src/core/public/chrome/ui/header/header_logo.tsx#L103
- Exit full screen button: https://github.com/elastic/kibana/blob/7.8/src/plugins/kibana_react/public/exit_full_screen_button/exit_full_screen_button.tsx#L68
- Loading screen: https://github.com/elastic/kibana/blob/7.8/src/core/server/rendering/views/template.tsx#L41
For the client side changes (everything with public as part of the path), you need to rebuild Kibana https://www.elastic.co/guide/en/kibana/master/building-kibana.html.