In Oedipus at Colonus, how can intonation be used to present one of the speeches of Oedipus?
Your question relates to a very important concept within drama, which is that of subtext. Subtext is the name that we give to the process that takes the script off the page and puts it onto the stage. Obviously, when we think of performing a drama, the words we say are only a very small part of what we need to think about. Aspects such as tone of voice, intonation, body language and the use of pauses as well as props, dress and lighting are all vital elements too.
However, what becomes difficult is that with all of these examples of subtext, we are left very often to interpret that subtext for ourselves. Sophocles did not produce a set of notes or a guide to tell actors how to deliver their speeches. Therefore, what you need to do is to think about your speech and its context and decide on that subtext for yourself. Based on the speech and its context, how would Oedipus deliver the speech that you have been given? Would he emphasise certain words more than others? What would different kind of intonations add or take away from that speech? What kind of implicit messages would be conveyed through the use of different intonations? Answering such questions will help you think through how you want to deliver that speech.
There is unfortunately no one answer, but this is also the joy of drama. You have to decide on intonation for yourself thinking about the kind of effect you want to achieve. Good luck!