I am playing Minecraft PE on an old world with no tall grass, and I'm not sure how to get wheat seeds. I've tried using a hoe on grass, but it doesn't work, and there are no villages on the map. How can I obtain wheat seeds in MCPE?
If your world is old and lacks the tall grass that is now required to obtain wheat seeds, what you need is bonemeal. Using bonemeal on a patch of grass will produce an area of tall grass (and some flowers), which can then be cut down for some seeds (if you have a tool enchanted with fortune, the drop rate of seeds from tall grass is higher).
Once you have some seeds, make some farmland with a hoe and grow wheat. Once the wheat is fully grown, harvesting it will yield seeds in addition to wheat, often more than enough to replant what you harvested, allowing you to grow more and more with each harvest.
In order to obtain bonemeal, you need to put bone(s) into a single square of the crafting window. To obtain bones; you can either kill skeletons, or go fishing. Getting bones from fishing may be rare, as they are part of the 'junk' rewards, which you only get 10% of the time on an unenchanted rod.