What is the independence day of Indonesia? And on which island is Jakarta located?

The Indonesian national day is 17th of August, the day Sukarno declared independence in 1945. You can read more about what happened in the article "The National Revolution, 1945-50" under "History".
From the article: On August 15, 1945, Japan surrendered. The Indonesian leadership, pressured by radical youth groups (the pemuda), were obliged to move quickly. With the cooperation of individual Japanese navy and army officers (others feared reprisals from the Allies or were not sympathetic to the Indonesian cause), Sukarno and Hatta formally declared the nation's independence on August 17 at the former's residence in Jakarta, raised the red and white national flag, and sang the new nation's national anthem, Indonesia Raya (Greater Indonesia). The following day a new constitution was promulgated.

Jakarta is located on West Java.