How Suit Actor can see when they shooting a fight scene?
 

Because look at the design at Kamen Rider Diend or any rider. It would be so hard for them to see thing when they shooting a fight scene

And as goe to Super Sentai, How can they see when they shooting a fight scene especially the Shinkenger's design. Shinkenger's helmet doesn't have a visor so how can they see?

Well, most of the fights are choreographed and practiced down to a T for the stunt actors that they almost don't need to see where they are, also some of the stunt helmets are drill with holes that they provide much needed oxygen access and can see pretty well

All of the helmets have at least a small window to see out of, although most of them only give the suit actor a very small and obstructed view of what's around them. With Kamen Rider, the eye holes are usually under the giant bug eyes (that's why most of the classic Rider helmets have those black "tear" designs - they're actually for the suit actor to see out of).

For Shinkenger the kanji is the visor as far as I am concerned

Easier in the 70s
 

Well it must have been easier in the '70s. The Goranger helmet designs had multiple little holes which probably account both for oxygen and sight. Even in the modern age when the Goranger suit designs have been reused, the holes are kept intact (even if it's only to maintain the integrity of the original suit designs). Or perhaps the nature of the suit cannot be kept the same unless the holes are transplanted every instance the suits are reproduced? Really, my wonder is the how the Mechas fight? Can they see in those warm and cumbersome costumes while prancing around a hot and packed studio? Also, how do spark squibs work? They freely have them on the suits and along the ground, and they don't seem to disrupt anyone despite the occasionally appearance of being painful. Could this get in the suit actors way or surprise them hard enough?

This is why suit actors are incredibly awesome.

Those are really the 'breathing holes'. :)

While they are damn awesome for what they do, the production crew has mastered the art of wearing spandex costumes with helmets by now and knows how to lessen the burden as much as possible. There's an extreme difference between a cosplayer trying to wear the suit and helmet and a suit actor.

Must be hard for a suit actor wearing Kamen Rider Baron's mask to see through with all the lines on his visor.

They ARE the visors. I'm not really sure what's the confusion there.