What is the suffix for do?

The suffix for "do" depends on what you want to form. Here are some options:

* -ing: This forms the present participle, used in continuous tenses: doing

* -er: This forms the noun that indicates a person who does something: doer

* -ed: This forms the past tense and past participle of regular verbs: did

* -able: This forms an adjective that means something can be done: doable

It's important to note that "do" is an irregular verb, so it doesn't follow the typical "-ed" pattern for the past tense and past participle.