My mom has dementia and I am having a difficult time reaching her. When I visit her, I have no idea what to say or how to 'wake her up'!

You can sing old songs, and talk about them yourself, eg how you heard them on the radio as a child. You can read to her, preferably something she might remember. I used to read to people in our local nursing home. They liked the awful old poems we learned in school (eg The highway man came riding, riding, riding, up to the old Inn door). Perhaps Hiawatha in your schools. My FIL in hospital went for 'The Man from Snowy River', good Aussie stuff, and the five other old VETs in the ward were straining to hear it too. My NH dears really enjoyed it when I read The Sermon on the Mount, from Matthew chapters 5,6 &7. I’m not a Church goer, but the language is beautiful and the sentiments are wonderful. In Church, you often just get snippets, not the whole thing. My people were nodding and smiling whenever some words came up that they remembered. Consider your visit as company and entertainment, not as a conversation, and it may be a lot easier.

Music is a good bridge builder when they are at the state of dementia where they just kinda stare off into space. You may not be able to connect her to any memories of you but she might liven up hearing old tunes from her teens and early twenties. Pops can't remember how to use a cell phone, who I am and has lost lots of other memories but he can still remember how to dance and loves music. Upbeat music to get him going, slow and easy to get him to calm down.

I'm not sure what you are asking, can you give any examples? Often people with dementia can't make connections because the pieces are missing, depending on her age there may also be hearing and/or vision loss that makes it harder to follow a conversation.