Hey, just joined the community. As a prior SideFx Games intern, I spent my months learning as much as the ins and outs of Houdini as I could.
Some of the essentials are their knowledge of attributes and their use cases. Since attributes allow you to determine everything from position of vertexs to direction of their normals. You need to know how to use these effectively. I.e a procedural folliage scattering tool needs to carry attributes with its scale and normals for its rotation.
Depending on the complexity of work required, what is their extent of knowledge of Vex the programming language in Houdini. This is one thing that still plagues me and can be essential for creating efficient tools. Check out Anastasia oparas work if interested in the highest standard possible for Vex.
Another thing that should be considered is can they set up and HDA (Houdini digital asset) and have parameters that an artist can understand and use. What are their practices and thought process behind setting up an HDA.
Middle level knowledge questions include: do you know how to use terrain height fields and the erosion techniques to get a realistic landscape. Can you make an art directable landscape. What is your workflow?
Do you know how to create a river that deforms the landscape. How would you go about creating it?
An interesting question would be what is your knowledge of creating destructible objects. Can they set up constraint networks. How would they create wood fracturing, metal breaking, concrete and brick destruction. All have different techniques to creating their constraint networks. Are they able to set it up to work in engine.
Are they able to collaboratively work on their tools with other Houdini artists. This can commonly be difficult due to wildly different workflows. How do they alleviate these issues.
How do they design to be user friendly and easily pick up and play.
How are they able to teach others to use their tools or ability to teach others to make their own tools. Are they able to debug someone else’s hip file.
I think thats a good set to ask. Feel free to PM with any other questions though!