What are the ongoing charges for Ireland-domiciled ETFs that are accumulating where dividends are automatically reinvested?

Depends completely on the individual etf.

currently the ETF annual fee (TER) range is 0.04% to 0.88%

You could look this up on www.etf.com with many search filters.

Make sure to select on the drop down menu Germany or UK at the head of the webpage to have more possible ETFs​​​

The dividends will be subjected to a 15% withholding tax even if the ETFs are accumulating!