What fallacy is this? Dictators support attacks on journalists. Therefore if you attack one journalists opinion, you are pro-dictator.

There are two significant problems with this argument. The first is use of the term "attack." It can be reasonably assumed that the arguer is referring to physical attacks on journalists of the dictators. In the second use of the word "attack" the arguer is specifically referring to "attacks on opinion," which quite different from chopping a journalist into pieces or similar (the implied use of "attack" by dictators). This is the equivocation fallacy<>.

The second problem has to do with the form of the argument:

(If you are a) Dictator, (then you) support attacks on journalists.
Therefore, if you attack one journalists opinion, you are pro-dictator.

the form being...

If P then Q.
Therefore, if Q then P.

Another example of this is:

If I have herpes, then I have a strange rash.
Therefore, if I have a strange rash, then I have herpes.

One can obviously have non-herpes rashes.

This is the fallacy known as Commutation of Conditionals where we are switching the antecedent and the consequent in a logical argument.

{date-time stamp}Saturday, Mar 09, 2019 04:59 PM{/date-time stamp}
I took a little artistic license by referring to this as a Commutation of Conditionals Fallacy because, as pointed out to me, the propositions used are not exact, which is required in a formal argument/fallacy. See my comments below as to why I think this fallacy works well for this example.