| jof | SmartCAM Job Operations File |
| joh | Zero 88 Jester ML Update Help Data |
| joined | HJSplit Data |
| joml | JOOB Object Modelling Language Data |
| jor | Microsoft SQL Server Journal Data |
| jos | Zero 88 Jester ML Software Update Data |
| jou | MSC Patran Journal |
| journal | Nuance Equitrac Cache |
| joz | JOSM Session Data |
| jp | Java Japanese Font Properties Data |
| jpegenx | Egis Encrypted JPEG Data |
| jpegx | Egis Encrypted JPEG Data |
| jperf | JPerf Data |
| jpgenx | Egis Encrypted JPEG Data |
| jpgs | CyberLink Power Media Player Data |
| jpgx | Egis Encrypted JPEG Data |
| jpi | Jupiter Filled Forms Data |
| jpm | Optifine JSON Part Model |
| jpn | PhotoModeler Lite Data |
| jpn | Unreal Engine Japanese Language Data |
| jpn | Windows Japanese Noise-word List |
| jpo | JPO Data |
| jprint | JasperReports Print Object |
| jpx | jAlbum Image Info |
| jpz | Crossword Puzzle Solver Data |
| jqx | Windows Help Related Data |
| jqz | JQuiz Data File |
| jr6 | AGICO JR-6 Spinner Data |
| jra | AGICO JR-5 Spinner Data |
| jrb | OpenNMS JRobin Database |
