What an interesting novel to discuss! I can see why you asked the question, though, because the content of this work of literature is so vast (and often so esoteric) it's hard to know where to start. I do wish I could know the context of the discussion, however, in that it would help me to figure out how to hone the discussion. For example, presenting the novel to an advanced literature class in a university would be different than presenting it to a high school history class or a simple book club or a venue for counselors learning about methods to help suicidal clients. This being said, I will assume that you are discussing the novel due to its literary and historical significance and go from there.
How about beginning the discussion with one of the most pertinent quotations from the book?
For thirty-five years now I've been in wastepaper, and it's my love story.
This gets right to the meat of the matter: literature which is socialism's "trash" has become another man's (Hanta's) "treasure" and, even further, his "love." Directly from this quote, we can discuss from the simple and leading to the more complex. I would suggest going from what it means to be "in wastepaper" and then what it means for it to be Hanta's "love story."
Lead the discussion into what it means for Hanta to have "been in wastepaper." This will flow nicely into the historical significance of the novel. Living in Prague, Hanta has been employed as a "paper crusher," or someone who is asked to get rid of banned books under direct orders of the socialist order in regards to censorship. Hanta, instead of following orders, saves the books, reads them, and learns from them. Hanta describes all of his methods in regards to his work and "failure" to do his work. All of these are worthy of discussion.
You can further lead your audience into discussion by reviewing the second part of the quotation above: the idea of the banned literature being Hanta's "love" and how these inner thoughts can be a good example of Stream of Consciousness Technique in writing. It is metaphorical to speak of Hanta's love of literature as a "love story."
My education has been so unwitting I can't quite tell which of my thoughts come from me and which from my books, but that's how I've stayed attuned to myself and the world around me for the past thirty-five years.
Here Hanta, again, describes his relationship with the literature in love language. It reminds me of that common image of a man and a woman holding hands, not knowing whose fingers are whose. The works of literature that Hanta has "saved" and "fallen in love with" and learned from are not an actual person that is able to express love, so to describe the relationship as "love" is most certainly a metaphor. In fact, Hanta often uses metaphors and ethereal description within his inner thoughts. Sometimes this actually confuses the reader, so it's a good time to mention the beauties (and the challenges) of this literary technique. Sometimes a character's meditations and imaginings don't mirror our own. For example, take this excerpt:
I can be by myself because I'm never lonely; I'm simply alone, living in my heavily populated solitude, a harum-scarum of infinity and eternity, and Infinity and Eternity seem to take a liking to the likes of me.
If you would like even further discussion, you could lead your audience from here to the idea of a method of escape from the socialist order and/or the specifics of the politics in Prague at the time. On the other hand, you could delve further into the idea of savoring literature by focusing on yet another quotation:
Because when I read, I don't really read; I pop a beautiful sentence into my mouth and suck it like a fruit drop, or I sip it like a liqueur until the thought dissolves in me like alcohol, infusing brain and heart and coursing on through the veins to the root of each blood vessel.
Generally, students of literature have been moved somehow or other by words of authors. Perhaps you could ask the question, when have YOU "pop[ped] a beautiful sentence into [your] mouth and suck[ed] it like a fruit drop"? You can begin with your own and have the members of your audience share. Such is a way to end your discussion leaving a wonderful taste in the mouths of your listeners.