I don't really know what your problem is. Do you have course lab manual to refer to, and just follow the procedures or do you have to plan the experiment yourself?
If you only need to qualitatively determine if these ions are present in the solution, alberto has given a lot of information. If you need to determine the concentration as well, I'd say you may need to do some titrations or anion chromatography. For Cl- and SO42- the metod is called precipitation titration, in which you might use autotitrator. Not sure about I- though.