Hi,
It is quite easy to save squash seeds. From a completely ripe squash take out the seeds, clean them as best you can, and then let dry spread out on paper towels.
The harder part about saving squash seeds is making sure they will come true the following year. Squash cross easily with other squash. Banana Pink Jumbo though is C. maxima which is not as readily grown by the average home gardener so there is less chance of incurring a crossing. C. pepo (zucchini, yellow squash, spaghetti, acorn, ornamental gourds, and some pumpkins) is much more popular and crossing happens quite frequently.
Remy