Siemens are a German company and the withholding tax is made up of
German Dividend Withholding Tax of 20% and a German Solidarity surcharge of 1.1%.
In relation to a refund, that depends on the existence of a double taxation agreement. If you are an Irish resident,then you can reclaim 5% of the 20% back from the German Tax authorities.
You will be liable to Irish Income Tax at 20% or 42% but the German Tax of 15% can be offset against this - I don't know whether the surcharge of 1.1% can be - ask the Revenue.
Hope this helps.