I am afraid you cannot get good answers with a domestic oven because the heat unaccounted losses are (i) large (ii) difficult to estimate even approximately. Your microwave idea (to which I had responded) was a more feasible method.

Olusegun,

Build a well-insulated container, pour in the liquid, immerse an electrical heating element in it, and a thermometer (or two). Drive the heater, record the temperatures, fit straight lines, and you'll probably have something that isn't off by more than 20% or so.

How accurately do you need to know these data?

You need not use domestic oven for determining heat capacity. Try to make a simple compact insulated container with a reliable temperature monitoring system as suggested  by Dr. Garry. That will solve your purpose.

Must you use an oven? if yes, you may have to ensure a more compacted (relatively of small size) type so that your liquid container will occupy a tangible space inside it. weight the the mass (m) of the liquid, witch on your oven and start heating. determine the starting and stopping temperature (T1 and T2 respectively) from the thermostart of the oven and time differentials [(dT) =stopping time (t2)-starting time (t1)] by which the oven was switched on during the heating process. Finally, note the current (I) and voltage (V) supplied to the heating element from the electrical source.

Then apply, C=IVdT/m(T2-T1), C=specific heat capacity

but if No, you could have better to used clorimeter method or resistor's method. As for calorimeter method, weight an empty calorimeter well lagged and put your liquid inside it. reweigh and substract the initial weight of calorimeter (to determine mass, m of the liquid). then cover and insert a thermometer through the lid. connect to the terminals of the calorimeter coils inserted in  the liquid of a variable power supply. switch the supply on to heat the liquid. note the I and V readings for the process. Record the temperature and time change dT and dt. finally, apply the above formular to determine C

for resistor's method, connect the terminals of a voltage supply (V) to resistor with a known resistance, R (ohms).  witch the supply on and record the temperature and time differentials. use the formular as before. instead of IV, use v*2/R