What skills would you recommend a 28 y/o pickup to remain relevant and useful in the workforce?

As a start, I would say communication skills. It's important to know how to interact with people to understand more from their point of views. In terms of hard skills, I would say digital marketing as it can help to generate new leads for your company as well.

1. how to be persuasive

2. how to influence people and make friends.

3. how to give public talks

These are soft skills that you can learn and experience from books and slowly practise it in your daily lives. These are skills that top billionaires and multimillionaires look out for, and will assist you in any corporate life that you seek. Or self-employment as your own business man.​​​

The most difficult skill in a workplace to master is anything pertaining to human beings.

Courses equipping you with tactics to manage workplace grievances, better a company's productivity through better compensation & benefit practices might be useful for your HR role. Pretty sure your company would be willing to have such courses for you sponsored.

Check out some SkillsFuture courses you may be interested to take up. On a side note, I reach out to HR practitioners like yourself to conduct seminars pertaining to legal education about Wills and Lasting Power of Attorney (LPA) which are complimentary for employees and organisations. Let me know if you are keen to have this arranged for your organisation as part of your HR initiatives in 2020 :)​​​

Depends on your interest. Hybrid jobs are a thing in future so data analytics,coding, designing etc will be popular. Having both skills will allow you to command higher salary as well, and your future job will be less likely to be automated.