From a discussion with 100 top CMO in 2016, Constellation Research based in Silicon Valley defined in 2016 the top 20 modern marketing challenges (not in order of importance).

Delivering on a creative to commerce vision
Improving marketing automation and optimization
Adjusting to fragmentation of channels, segments, and trends
Investing in audience development
Targeting with precision and less false positives
Dealing with data driven approaches
Building for intention driven design in customer experience
Developing in-house ad networks and programmatic strategies
Mastering data and data management platforms
Re positioning the corporate brand for a digital world
Empowering communities and audience development
Attracting and retaining the right skill sets for digital marketing transformation
Identifying new agency and consulting partners to augment efforts
Improving internal employee engagement
Building a culture of behind the brand promise
Creating a P2P model
Aligning marketing strategy with marketing technology
Proving ROI
Crafting compelling contextually relevant content
Getting ahead of the latest disruptive technologies