I want to convert my shp layers into one DGN file using ogr2ogr (QGIS). When I use this tool, I can only select one layer to convert. My problem is I don't know how to select all three layers at the same time and converting them into the same destination dgn file.
According to the OGR Driver Info for Microstation DGN, you cannot create DGN file consisting of more than one layer:
DGN files can only have one layer. Attempts to create more than one layer in a DGN file will fail.
So I don't think this is possible through ogr2ogr or QGIS. You may need to look for another application.