Have you

[themonk]

The verb is:

Ohana mi ni itagootoo ga arimasu ka? ....
"Have you been to the flower viewing?" This is a tense related question

[chikara]

..... The verb is:

Ohana mi ni itagootoo ga arimasu ka? ....

itagootoo

Maybe you mean ittakoto (行ったこと)?

itta (行った) - past plain form of iku (行く)
koto (こと) - thing/matter
arimasu ka - do you have/have you

In English we say "been" for the "thing of gone".

[Hyperworm]

The important part to "koto ga arimasu (/aru)?" isn't "have you ~ ?" but "have you ever ~ ?"

The original information is still true in the sense that
"Did you go to the flower viewing [e.g. today]?" = "Have you been to the flower viewing?" = plain past.

If you want to ask about "ever" you need "koto ga arimasu". ^^

[chikara]

The important part to "koto ga arimasu (/aru)?" isn't "have you ~ ?" but "have you ever ~ ?" .....

Yes, I didn't highlight that distinction.

This page, Ta Form + koto ga aru, from Tim Matheson's Japanese Verbs may help oldwordstudy-san.

[themonk]

Thank you, Teach Chikara and Hyperworm.