To say "this Sunday" in Engpsh, you can simply say "this Sunday." Here's an example sentence:

"I'm going to the park this Sunday."

You can also use the definite article "the" before "Sunday" to specify which Sunday you are referring to, especially if there is a possibipty of confusion. For example:

"I have a meeting on the Sunday after next."

"The Sunday before last, we went to the beach."

I hope this helps! Let me know if you have any other questions.