Q: Mac OS 9 Installation Disc.

Usually the correct disc you'd need would be the install-restore DVD set

the computer came with, when new. All the compatible software it could

run was included in the retail package the computer shipped with; then

any other update bits were to be downloaded from the Software Update.

A retail DVD OS X install disc newer than the system in the computer

may be used to start (boot, with C key held) the Mac and then there

are options in the Installer menu bar once it is running the computer;

from there Disk Utility and other items can be used. Assuming OS X

systems are the primary boot, and OS 9 would be seen under Classic.

Depending on the identify of your iBook G4, the latest OS X system it

may be able to run - if the processor is greater than 867MHz - is 10.5.8.

To obtain a replacement disc, you may have to look online at auction or

amazon resellers, or second hand stores, schools who are upgrading

their systems & software sometimes sell them; plus online resellers of

vintage Mac parts and systems are also places to check.

For version information, compare the specs of your iBook G4 with those

models in EveryMac.com, also iFixit.com has guides that can be helpful

to update, upgrade, repair, etc various Mac models. MacTracker.ca has

a database to download for offline use. And Apple Support still has some

vintage information on older hardware, plus a little about obsolete, too.

You'd likely need to correctly identify the iBook G4 exactly in order to

know the details of what it should've had with it, and what it can run.

Also the hardware may need an upgrade to run a later OS version.

Some sites such as powerbookmedic have a secure page to lookup

your product by Serial number, or a Model identifier number:

https://www.powerbookmedic.com/identify-mac-serial.php

Hopefully this helps.

Good luck & happy computing!