Château de Moidière is in the rural village Bonnefamille. In most rural places such as this one, public transport caters for schoolchildren and to some extent to residents, rarely to tourists.
France doesn't have a central place to find transport information, and most of the information, when you manage to find it, is in French. For train schedules, visit the regional trains website, here for Rhône-Alpes. For bus information, visit both the site of the région (Rhône-Alpes) and the site of the département (Isère, follow the link to Transisère). A web search like “cars Isère” will usually find the right site (cars is French for “intercity buses”).
The nearest train station is down in the valley (~10km away with a ~100m climb) in La Verpillière, which is on the Lyon–Grenoble line and served by half-hourly trains on weekdays, hourly or more on week-ends.
According to the map, two bus lines go through Bonnefamille. A search by township lists more lines, but I think it includes lines in the vicinity. Line 2990 connects Vienne on the Lyon–Valence train line with Bourgoin-Jallieu on the Lyon–Grenoble line, with a stop in Bonnefamille about midway. The bus stops at Villefontaine Parc Technologique Ouest which is about 1.5km from the train station in La Verpillière but it isn't clear to me that this would save time. It runs only on weekdays and there are even fewer buses during school holidays.
There's also 2070, and 2960 (situation map) from Lyon Part-Dieu (~1 hour) but the Bonnefamille stop is at the other end of the municipality, about 2km away; the Quatre Routes stop in Diémoz is slightly closer.
Alternatively, you could take a taxi in La Verpillière. Since this isn't a very big town, you may want to book first, which is likely to require a phone call in French. Online estimates show the price at ~20€.
The other option is to hitch-hike. Going there, it might be difficult to find someone going in the right direction. But coming back, asking visitors who came back car to drop you down at a mutually convenient train station is a good option.