"i always know how to surprise"

What exactly are you trying to portray? "I always know how to surprise 'you' " makes sense in a thoughtful way. Implying you know the ways to surprise a friend or girlfriend.

I’m not sure what this is meant to convey. is this flirting? as the sentence is formed now, it sounds like someone bragging that they are good at surprising people in a playful way. “I didn’t expect this from you!” “What can I say? I always know how to surprise.” 😏

to surprise is a transitive verb. You can't say "I surprise", you gotta say that you surprise SOMETHING. For example, while I always surprise doesn't work, I always surprise you does.

The modifier "always" could 'more correctly' go in front of the word 'surprise.' By putting it in front of 'know' you're suggesting there was never a time during which you did not know this, which is a strange thing to say. Rather, you're likely trying to say you can surprise people whenever you wish, in which case the adverb modifier 'always' should be in the position closest to the word it modifies (again, "surprise"). I would note, however, that this sounds a bit stiff and awkward in conversation though it is logically consistent.