Please explain 'if' and how paraphrase it.
Now, researchers aim to learn if and how animals can really enjoy their lives.
That form is collapsing two statements into one:
They aim to learn if animals have fun.
They aim to learn how animals have fun.
It is usually expressed as follows, so as not to make the how-clause a foregone conclusion:
They aim to learn if, and if so, how animals have fun.