Thanks for your quick reply!
1) Implementing the GEW as a "Visual Placements" Item works quite well, if you define the whole svg as an area and then transform the marked svg position coordinates into Emotion/Intensity labels later, e.g., in R. A drawback is that participants may still select the different intensities of the same emotion, e.g., choosing happiness in intensity 4 and intensity 6 simultaneously. However, this may work as an initial solution.
2) Following the instructions "Use Custom Form Elements" I stuck at element 3 "Create a new text element in Text Elements and Labels". I created a text element (GEW), selected HTML code and inserted the HTML-code to generate the SVG-Graphic to start with. The error feedback says "Tag svg:xxx" invalid. The link to the questionnaire is https://www.soscisurvey.de/GenevaEmotionWheel/. This Item is on page 3.
3) I started the questionnaire in preview mode and forwarded to the page presenting GEW as "SVG as selection (multiple)" (Page 2) and searched for "registerMarker(" in the HTML file. I could not find the function there (only SoSciTools.registerFocus();) and also not in the included scripts polyfill.js, SoSciTools.min.js, S2Selection.min.js, S2SVGSelect.min.js, SoSciEnhancedInputs.min.js -> where should I look for this function? How can I change / upload the extended (122 instead of 100) markings?