Have a look at the Data Loading Tutorial 3.
There you can see, how to create and use your own Dataset.
From the code you’ve posted, it looks like you already have a Dataset for your gaze data.
You can just wrap this Dataset into a DataLoader and use it to get your samples:
dataset = MPIGaueDataset(subject_id=..., dataset_dir=...)
loader = DataLoader(
    dataset,
    num_workers=...,
    shuffle=...
)
    
for image, pose, gaze in loader:
    # Your training routine