Your choice of a problem to address is wide open. However, a number of suggestions and pointers follow, which are intended to steer you in a worthwhile direction. Whatever problem you address, you must collect information from at least 100 gravestones. The problem which you approach will be either synchronic or diachronic. You might choose to look at some aspect of mortuary variability within the period 1900-1920, for example.
Diachronic research looks at changes in behaviour over a longer period.
Attached to this assignment you will find a description of seriation which you may find useful. You will not have time to record all of the information in your chosen section of the cemetery. Therefore, you must determine a method of sampling the gravestones. Record every tenth stone, or all stones in every tenth row. Whatever sampling strategy you use, you must describe it clearly in your report.