You need IsoBuster for this. Make sure underside of faulty CD is as clean as possible and insert into CD drive. Put your CD into drive and wait for drive light to go out.
Open Isobuster and if you have more than one CD drive select drive. You should see some folders/files picked-up. Wait for the drive light to go out. Be patient it can take quite a number of minutes if there are a lot of files. There is a Refresh button if needed but it will incur a time loss.
In the left window right click on CD icon and click on Find missing files and folders.
Click Yes in window that appears. Click OK in next window that appears. Extract file in folder of your choice. If the file already exists then overwrite it.
If the next window is Incomplete image file then click OK. Two files are produced "cd.ibp" and "cd.ibq".
You should now see more folders/files in Isobuster. Click on the black icon having UDF in green letters. You should be able to see some folders/files which contain your missing data.
Right click on this UDF icon and click Extract PacketCDxx (or Session x). Save in a folder of your choice.
Also look in the last folder having a black icon having UDF in yellow letters. If there are files then right click on this UDF icon and click Extract PacketCDxx.
Save in a folder of your choice. The total number of files in each folder is shown on the Status bar at the bottom. It is better to exit Isobuster after completing a CD and then re-opening Isobuster for the next one.
The first folder saved with green UDF icon should have the best files, if the number of files in the folder saved using the yellow UDF icon is higher then copy over the extra files into the first folder.