Learn Turkish: Bu filmi mutlaka izlemelisin. - You must certainly watch this film.

The suffix -i is the accusative case, which marks a specific direct object. Because you are pointing out a specific movie by saying this film (bu filmi) rather than just any film, it requires the -i ending.

How does the verb izlemelisin break down?

It is made of three parts: izle (the verb root meaning watch), -meli (the necessity suffix meaning must or should), and -sin (the personal suffix for you). Put together, it means you must watch.

If izlemelisin already means you must watch, isn't the word mutlaka redundant?

Not at all! While the suffix -meli provides the grammatical must, adding the adverb mutlaka (absolutely or certainly) gives the sentence extra emphasis. It turns a standard recommendation into a very strong one.

Could I change the word order and say mutlaka bu filmi izlemelisin?

Yes, Turkish word order is flexible. However, words placed immediately before the verb get the most focus. Putting mutlaka right before izlemelisin strongly stresses the absolute necessity of doing the action.