Assuming you are using Qlik Sense Enterprise (Server), you won't be able to see the script unless you "own" the app and it is in your "my work" stream. If you have sufficient rights you can copy your colleagues app such that you have a copy in "my work" or you can take ownership of the app. If you don't have the level of access required to do this you will need to get an administrator to assist.
If you are using Qlik Sense Desktop then Mauri's advice is correct.
For future reference, it helps us to help you if you can tell us exactly what product and version you are using.
The data load editor is not available in published apps, it is a basic security feature. However, now that you have appropriate access (assuming your implementation of the default "content admin" role hasn't been modified and isn't being overridden by another rule) you can take a copy of the app to work with in your "My Work" stream.
Do you have a copy of the app in your "My Work" stream? If not, now that you have appropriate access you should be able to take a copy of the app by right-clicking / long-pressing on it and selecting "duplicate". Alternatively, if you can access the QMC go into the Apps section, locate the app you wish to examine, select it and then use the "more actions" button to duplicate the app.