There are different parameters you can use, but as the question is not clear what exactly you want to do , I think with EEG and Task Load Index (TLI) you are good to go.
The Task load index (TLI) is the so called engagement-index and is
defined by two formulas, TLI1 and TLI2. However, these indices
were calculated as follows:
where Pθ and Pα denote the theta- and alpha-band power, respectively.
Pθ,Fz and Pθ,AFz are the theta activities of Fz and AFz electrodes
respectively. The θ (theta) activity was calculated by averaging the
power spectrum of the θ frequency range (4-7.5 Hz). Similarly, Pα,Pz
and Pα,CPzPOz are the α (alpha) activities of Pz and the pool of CPz
and POz electrodes, respectively. The α activity was calculated by
averaging the power spectrum of the α frequency range (8- 12.5)
This section is exactly quoted from this paper.