EDIT: On Tap is closed Monday, Tuesday, and Wednesday. I can’t see info one way or the other about the Brass Monkey. I believe I saw signs at Redpoint last week saying they were closed for at least one of the CNY days.
Here are the hours for the Tianmu Sogo, with the restaurant floors being open both evenings: to me that suggests you’d be fine at most department store restaurants. Although Dingtaifeng is closed.
Since @lostinasia mentioned Tienmu Sogo, I’d add that Fuxing Sogo will also apparently be open every day. This is helpful as the Joel Robuchon outpost in the B3 level is a great place to pick up bread and take-out items like salmon quiche (made with kampot peppers from Cambodia—wow!) and ham and cheese sandwiches (these guys make their own ham and of course the bread is baked in house). The cost for these culinary wonders? NT$150 and NT$200 respectively. They will have my business—sorry Marco, no KFC for me.