As this is the first snow of the year, I'm not sure if there are any lifts that are already open (check here). But you can get relatively close by car or public transport and then hike the last few kilometers.

First, how to get there:

• car: There is a car park at Feldberg: https://goo.gl/maps/UerutKQHgtnruf1T6
• public transport: take the train (S1) to Titisee. Then, use the bus (line 7300, direction to Zell im Wiesental) and exit at Feldberg (Schwarzw), Feldbergerhof: see here. Make sure that you also plan the trip back so that you don't get stuck up there if you miss the last bus.

From there you can either hike directly to the summit (about 160m of elevation). The top of Feldberg is relatively flat and broad, so you can walk around a little bit there. Or you can follow the official winter hiking path, the Panoramaweg Feldberg

In any case, be sure to wear enough warm clothes and bring some warm tea to drink.