For the EF, how can you tell which feasts will be celebrated if they fall on a Sunday, and which will not? Is there a particular class of feasts (like All Saints) that is always celebrated if it falls on a Sunday?
Above all, it's best to ask the priest, primarily because he might be following a different Ordo, or he might know of local feasts or customs, or he might even be following an older set of rubrics.
Otherwise, it is probably easiest to consult an Ordo yourself. The FSSP provides one that you can order online. The Latin Mass Society (UK) publishes its Ordo online.
If you're asking for a future year, the short answer is that it depends on the Sunday - some are I Class and some are II Class. And there are tables of precedence in the rubrics to consult.
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