Hi guys. Just wondering how one might say "Where do I start?" in Irish.

Or similar phrases like "Where shall I start?"

grma!

Cá dtosnaím?
Cá dtosnóidh mé?

Cén áit a dtosóidh mé? (GC) "Where shall I start?"

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

I hadn't even thought of using áit. Is it required so as to specify a physical place?

I'm not sure you can use cá and cén áit / cá háit when not talking about a place.
I'f you're asking how you should start learning Irish, for instance, I'd rather use a word for "how", conas/cén chaoi/goidé mar...

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

I think using cá is fine with the implication that you're talking about "where to a book/info etc.". Of course your suggestion makes sense too.

Both are are correct.

You can use "áit" without it being a geographical place.

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It is recommended that you always wait for three to agree on a translation.
I speak Connemara Irish, and my input will often reflect that.
I will do an mp3 file on request for short translations.
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GM

Cá dtosnód/ Cá dtosód?

GM

Another that I have always used in preference is:- Cá dtosóidh mé

I like this too! It was also my suggestion; which is the standard one, tosnaigh, or tosaigh? (standard spelling I mean).