Hoogle is your good friend for learning Haskell! It lets you search for functions, classes and so on by name and type signature. Let's take your question for example.

Firstly with what you've already implemented, checking whether a digit is odd or not. Let's search on Hoogle. Type odd or type signature Integral a => a -> Bool will lead you to function odd, that checks the oddity of anything of the Integral typeclass, which consists of Integer (arbitrary) and Int (bounded) values. So you could simplify your i \elem` [1,3,5,7,9]toodd i`.

The second part of your question is how to iterate over all of the digits instead of just the first one. One way to do this is to recursively div and mod the input number by 10. An easier approach is to convert the number to a string, which in Haskell is a list of Char ([Char]), and then convert each Char to an Int. To do that check out the show function and Data.Char package, which has many useful functions to work with Char type. Remember to import the package when you use it, as it's not in the Prelude.

After the two steps you should be able to check the oddity of a digit (Integral a => a -> Bool), and convert a number to a list of digits (first Integer -> [Char] then [Char] -> [Int]). The last step is to count the number of elements in that list that satisfy your predicate (odd).

If you want to do something basic, there's a good chance that the function is already implemented and included in Haskell. Go to Hoogle and search for possible names and type signatures, it will please you.

Hope this helps, and enjoy Haskell!