"Now he is not wearing a hat."
Translation:Nu draagt hij geen hoed.
Because as Dutch is a V2 language, the verb must always be the second element/constituent in a main/independent clause, which means that if you start your sentence with something other than the subject, subject-verb inversion occurs.
For instance, if you wanted to tell a friend that every morning you drink a cup of tea, you'd say:
'Elke ochtend drink ik een kopje thee.'
In this example:
√ elke ochtend is the first element/constituent,
√ drink, being the verb, is the second,
√ ik, the subject, is the third, and
√ een kopje thee, the Direct Object, is the last constituent (just in this case).
Hope this helps.
The Dutch present progressive ("is aan het ...") is not used very much, and only for ongoing actions. It sounds weird to use it with the verb "dragen", since wearing something is not really an action.