A "planted question" refers to a question that is asked at an event or interview by someone who was specifically instructed to do so. The question is typically planned in advance to serve a particular purpose or agenda. Full definition
That's why the Tory whips in the Commons were planting questions about me for David Cameron and abusing their parliamentary privilege to say I supported terrorism. (theguardian.com)
Far from gaining «credibility», it's simply given the impression that Labour are admitting they overspent when they were in government (in which case, why would people want to put them back in government again if they feel even Labour are admitting they're econonomically - incompetent), while also planting the question in people's minds about what the point in voting Labour is if they're just going to do the same as the Tories. (labour-uncut.co.uk)
ALBANY — Gov. Andrew Cuomo decided to take questions from the Albany press corps by phone rather than in person on Thursday, even though he was in the capital city, and his aides contacted several reporters in hopes of planting questions with them. (politico.com)