Hi Lowri,
Day to day no.
The British Legion have in recent years took the mantle of opening the Arch to members of the public. They may well be a good port of call
http://counties.britishlegion.org.uk/counties/wales/membership/north-wales-districtThe Arch is part of Bangor University's estate, it is in their trust, they have the keys! so they may also be worth contacting.
http://www.bangor.ac.uk/corporate/contactus.php.enYou will find it open on Remembrance Sunday each year. One organisation or another (sometimes the Civic Society) volunteer to staff it.
The panels are online here:
http://www.bangorcivicsociety.org.uk/pages/arch/index.htmThe memorials inside are online here:
http://www.bangorcivicsociety.org.uk/pages/hisso/archmems.htmThe only other thing to say is that there is a large building project directly behind the arch and the resulting building work etc may impact the University's desire for it to be open at the moment.
https://www.pontio.co.ukHope that helps
Matt