There'll be plenty of jobs. What there won't be will be employee positions. Companies will increasingly replace employees with robotics and software. Work will shift to self-employment. A contract software engineer will contract with an accountant to handle accounting, with an advertising firm to handle ad placement, with their hosting services to handle routine administration of their servers and so on. An author would contract with someone to screen calls and mail and act as a secretary/receptionist, with someone else to proofread and edit their manuscripts and so on, and would publish directly through distribution channels like Amazon's Kindle Store. A seamstress would contract for advertising services and for janitorial services for the store. Lots of work, but no employees.
My argument in favor of basic income is that starting all of that requires a certain stability. You can't start a contract software consulting business, or start writing full-time, or start a dressmaking store, if you're scrambling to keep food on the table and a roof over your family's head. You can't get a full-time job to cover the bills because those full-time jobs won't exist. So what's the alternative to a basic income if you want people to work? If it's not there they won't be able to afford to spare the concentrated effort needed to get a successful business off the ground, it'll all be sucked up by the scramble to get enough cash this week to buy groceries. If they put in the effort, their family'll be out on the streets and starving in the time it takes for the effort to start producing results.