Translation:मैं खाता हूँ।
I don't think this is the only translation. A woman should say "खाती", not "खाता", however I got both as the choices. I'm not sure whether both will be marked as correct, but still, the exact form of the verb depends too much on the particular user, so people may be left wondering which one to use.
I don't know either, closest I can get is हूॅं (notice bindu is next to the candra, not inside) by selecting candra diacritic from page 4, ha from p1, and then the bindu and ū also from p1 (which by now shows the complete character like that, not the bindu alone).
I can get the candrabindu correct by abusing ् , but then the ह ends up next to it.
Snell says some people write just the bindu instead of full thing, so perhaps Google Keyboard only supports that? हूं is made much easier to type (हू is a suggestion as soon as you type ह, then हूं is a suggestion as soon as you accept that).
The diacritics one is called Inscript and is basically the layout of the qwerty keyboard (it has the same order as a physical Hindi/international keyboard), the other devanagari keyboard has the letters in alphabetical order (first row is the vowels, then a row with velar consonants क ख ग घ etc) which makes much more sense when you are learning the script.
First, select the correct keyboard. A search for Hindi proposes 3 keyboards: Choose Hindi India (not Fiji keyboards). Then you can select up to 3 'subkeyboards' (my term, not android's). Don't pick the ones called English (abc-> Devangari) or "compact" (maybe the latter also works, but I dunno how).
Using the keyboard: on the first page, select ह. Above the main keyboard area (ie where suggestions usually appear), blue text pops up. There you can see all possible combinations of this consonant with vowels: हा हि ही ही हु हू etc. Pick हु (don't worry about the line crossing the vowel; it'll vanish). Then go to p. 4 of the keyboard and select the diacritic that belongs above the vowel. Voilà! हुऀ
It would be nice if someone could post these instructions in the help part of the Duolingo website (I only have the app). Perhaps someone else can add instructions for using the "compact" keyboard (which I guess also works).
Thank you for describing the process in detail. However, the correct combination character to pick is हू and not हु . The diacritic from page 4 is ऀ , and what you need is ँ. It is actually on page 1, upper right corner. As we have already chosen the combination character, you’ll see हूं instead of ं . Press and hold to get हूँ .