For example, suppose a German native is walking on a road but does not know the word "die Straße" (so she also doesn't know the noun gender). She then points down at the road says, "I walk on it." What is the German equivalent in everyday conversation?
German native speakers often use the word das Ding for things whose name they don't know. Examples:
Ich habe das Programm geöffnet. Muss ich jetzt hier auf dieses Ding klicken?
Sometimes it is altered to das Dings or even Dingsbums as mentioned in Konstantin's answer:
Zum Kochen von Kartoffeln benutze ich immer dieses Dings.
As das Ding is neuter, one refers to it with es. Continuing the above conversation:
Wo hast du es gekauft?
This usage of Ding is informal and only used in spoken language, of course.
In conversations, many people also use dings as a fill word when they try to remember a name or word:
Gesten waren wir mit Anna, Flo und äh...dings...Fabian essen.
I understand the question as asking for a workaround that doesn't need a catch-all noun such as thing/Ding. I am guessing it is motivated by the fact that when translating
I walk on it.
to German you need to know what "it" refers to in order to find the gender.
Sometimes Germans use natural gender in this kind of situation. People and animals with an overt sex/gender are treated as if that's their grammatical gender (which it likely is anyway), and everything else is treated as neuter. This is probably one of the things that drive a language towards natural gender for everything -- a process that has already completed in English but that can be observed at work in standard Dutch and Flemish (and especially in the differences between the two).
I think it's a general principle in German that natural gender is always correct with demonstratives, though occasionally when it's clear what the correct noun would be, that can be used as well. E.g., the one over there translates to der/die/das da drüben according to the natural gender of whatever is pointed to.
But in this particular case we actually wouldn't normally use natural gender because there is a workaround involving a demonstrative that avoids the issue completely:
Ich gehe darauf.
English still has the same construction, though it's very antiquated nowadays except in specific (e.g. legal) contexts:
I walk thereon.
You could (colloquially) use the word Dingsbums for an object or name that you do not know